O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O B-Wavelength O O O O O O O B-Observatory O O O O O O O O O O O O O B-Wavelength B-Wavelength I-Wavelength O O O O O O O O B-Wavelength B-Wavelength I-Wavelength O O O O O O O O O B-Observatory O O O O O O O O O O O O O O O O O B-Wavelength O O B-Observatory O O O O O O B-Wavelength I-Wavelength O O O O O B-Wavelength B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O B-Observatory O O O O O O O O O O O O O O B-Dataset O B-Observatory O O B-Wavelength O O O O B-CelestialRegion I-CelestialRegion I-CelestialRegion O B-Observatory O O O O O O B-Wavelength B-Wavelength I-Wavelength O O O O O O O O B-Telescope O O O O B-Telescope O O O O O O O O B-Wavelength O O O O O O O O O B-Wavelength O O O O O O B-Wavelength B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O B-Person I-Person O O O B-Person O O O O O O O B-Grant I-Grant I-Grant I-Grant I-Grant I-Grant I-Grant I-Grant O O O B-Location B-Organization I-Organization I-Organization I-Organization I-Organization I-Organization B-Organization O O O O O O O O O O O B-Archive I-Archive I-Archive I-Archive I-Archive B-Archive O O B-Organization I-Organization I-Organization I-Organization I-Organization O B-Database I-Database I-Database B-Database O O O O B-Organization I-Organization I-Organization B-Organization I-Organization I-Organization I-Organization O O O O B-Organization I-Organization I-Organization I-Organization I-Organization O O O O O O O O B-Survey B-Survey I-Survey I-Survey I-Survey O B-Observatory I-Observatory I-Observatory I-Observatory O O O B-Organization I-Organization I-Organization O O O O B-Organization I-Organization I-Organization O O O B-Survey I-Survey I-Survey I-Survey B-Survey O B-Observatory I-Observatory O O B-Person I-Person O O O B-Person I-Person B-Person I-Person O B-Person I-Person O O O O O O O O B-Observatory I-Observatory I-Observatory I-Observatory B-Observatory O O O O O O B-Survey B-Survey O O O B-Person I-Person O O O O O O O O O B-Telescope O O O O B-Organization I-Organization I-Organization O O O O O B-Organization I-Organization I-Organization O O B-Organization I-Organization I-Organization I-Organization O O B-Organization I-Organization I-Organization O O O O O O O O O B-Telescope I-Telescope I-Telescope I-Telescope O O O O O O O O O

blazar-like counterparts of the UGSs. 3. We describe the statistically significant correlations between the γ -ray photon index and the mid-IR colors for both the whole sample of Fermi blazars and the BZB and BZQ spectral classes separately, the basis of the IR– γ -ray connection. This correlation appears “stronger” than the well-known radio– γ -ray connection because it involves the spectral shapes of the Fermi blazars over ∼10 orders of magnitude and not only their fluxes. 4. We argue that the peculiar mid-IR colors of Fermi blazars do not depend on their γ -ray photon index. In turn, the IR– γ -ray connection is unexpected. We have also highlighted its potential use to implement the search for blazar-like counterparts of the Fermi UGSs. 5. We show that a large fraction of the BCUs listed in the 3FGL whose WISE counterpart has mid-IR colors consistent with the WISE Gamma-ray Strip have Fermi spectral index values consistent with the IR– γ -ray connection. Taking advantage of the overwhelming fraction of Fermi blazars detected in the WISE all-sky survey (i.e., ∼99%) in the first two mid-IR filters, we suggest that a comprehensive investigation of their IR properties at the light of the IR– γ -ray connection described in this paper can represent a powerful tool to reveal the real fraction of Fermi blazars hidden within the sample of UGSs. We thank the anonymous referee for useful comments that led to improvements in the paper. We also thank J. Ballet for helpful discussions. F.M. gratefully acknowledges the financial support of the Programma Giovani Ricercatori—Rita Levi Montalcini—Rientro dei Cervelli (2012) awarded by the Italian Ministry of Education, Universities and Research (MIUR). This research has made use of data obtained from the high-energy Astrophysics Science Archive Research Center (HEASARC) provided by NASA’s Goddard Space Flight Center. The NASA/IPAC Extragalactic Database (NED) is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Part of this work is based on the NVSS (NRAO VLA Sky Survey). The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under contract with the National Science Foundation and on the VLA Low-frequency Sky Survey (VLSS). The Molonglo Observatory site manager, Duncan Campbell-Wilson, and the staff, Jeff Webb, Michael White, and John Barry, are responsible for the smooth operation of the Molonglo Observatory Synthesis Telescope (MOST) and the day-to-day observing program of SUMSS. SUMSS is dedicated to Michael Large, whose expertise and vision made the project possible. The MOST is operated by the School of Physics with the support of the Australian Research Council and the Science Foundation for Physics within the University of Sydney. This publication makes use of data products from the Wide-field Infrared Survey Explorer , which is a joint project of the University


O O B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject I-CelestialObject I-CelestialObject O B-CelestialObject I-CelestialObject O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O B-CelestialObject I-CelestialObject I-CelestialObject I-CelestialObject O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O B-Dataset I-Dataset O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O B-CelestialObject I-CelestialObject O B-CelestialObject I-CelestialObject I-CelestialObject I-CelestialObject O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-Model I-Model I-Model

5 5 TYC 1323-1592-1 (=LS 36; Stephenson Sanduleak 1971 ) is an O8 Vz star newly identified here. It has the narrowest line profiles among the LAMOST medium-resolution spectra of O dwarfs, hence, we assume ≃ 0; the exact value is of little consequence, as long as it is small (which is clearly the case). to estimate P ( λ ), which is the rectified intrinsic line profile without rotation. 2. For an assumed , we fitted the functionto S ( λ ), which is the observed He i λ 5016 profile for each ON star. Here, ⨂ is the convolution operator; is the rotational broadening function (Gray 2005 ); and are fit parameters. 3. A figure of merit, , was calculated for trial values from 180 to 400 at steps of 7 . A refined best-fit was finally obtained by fitting a third-order polynomial to the 11 ξ values about the smallest one for each star. To estimate (internal) uncertainties on the velocities, we assumed the best-fit model to be representative of the true profile, added Gaussian noise matching the observed spectra, and measured v R and v e sin i as above, repeating the process 10 4 times. Our final results for and are: (LS I +61 28) and (HDE 236672). The He i λ 5016 rectified observations and adopted models are shown in Figure 2 . If macroturbulence were more important in the target stars than in TYC 1323-1592-1, our values may be upper limits (Howarth et al. 1997 ; Simón-Díaz Herrero 2007 ), although rotational broadening clearly dominates for the rapid rotators. Figure 2. He i λ 5016 profiles of LS I +61 28 and HDE 236672. The red lines are the best-fit rotationally broadened models. We also measured the radial velocity of He i λ 5016, along with other lines of hydrogen and helium, in the low-resolution spectra at our disposal, and find no evidence for radial-velocity variability in excess of ∼20 (i.e., ∼0.1 of the resolution element). 3. Kinematics of Galactic ON Stars Gaia DR2 provides parallaxes and proper motions with unprecedented precision for more than a billion stars (Gaia Collaboration et al. 2018 ). By combining this information with radial velocities, we can determine the kinematics of ON stars in the Galaxy. In addition to the two new ONn stars reported here, we investigate all those ON stars satisfying the following criteria: (i) not classified as a supergiant, (ii) parallax accuracy of , and (iii) a radial velocity reported in Table 2 of Walborn et al. ( 2011 ). This sample is summarized in Table 2 . Other than for their rotation velocities, the dozen sample stars have similar spectral characteristics and similar effective temperatures (and thus may have arisen through similar processes). Table 2 Kinematic Parameters for the ON-star Sample Note. Spectral types (column 3) and binary indicators (column 10) adopted from Walborn et al. ( 2011 ), except HDE 236672 and LS I +61 28 (this paper). Projected rotational velocities are from Martins et al. ( 2015b ), Howarth et al. ( 1997 ), and this paper. In column 9, . We used Markov Chain Monte


O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model I-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O B-ObservationalTechniques O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O B-Wavelength O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O B-Wavelength O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

to calculate the percentage retention of Si and C by the mantle. Upon simulating the sputtering yield for two cases, one with a 0.02 μ m thick ice mantle and another without an ice mantle, we observe a higher number of recoils in the grain with an ice mantle. This shows that having an ice mantle accelerates the sputtering process and increases the collision cascade inside the grain. Due to the limitations of using Monte Carlo simulations, it is hard to arrive at the exact change in collision cascade due to the ice mantle. Nonetheless, the central point of this result is to emphasize the destructive nature of the ice mantle along with its protective nature when it retains the ejected atoms from the core. This increase might not affect the absolute value of sputtering; however, it makes the grain more amorphous. Also, for relatively slow-moving projectiles such as shock-wave-accelerated particles, there would be even higher amorphization. Most of the presolar SiC grains analyzed in the laboratory have been reported to be crystalline and even spectroscopically detected as a 11 μ m feature. The absence of amorphous SiC in both the laboratory and spectroscopically has been under discussion for the past two decades, mainly because the majority of presolar silicate grains studied in the laboratory have amorphous structure (Vollmer et al. 2009 ). Both amorphous and crystalline (10%) silicates have been observed around AGB stars and young main-sequence stars (Demyk et al. 2000 ). To understand the grain shape and size dependence on infrared spectra, Speck et al. ( 2005 ) compared IR spectra from various polytypes of SiC in the laboratory. This study indicated the possibility of a 9 μ m feature being related to amorphous SiC. As for the laboratory measurements, this difference between presolar silicates and SiC mainly arises due to the different identification/separation methods. Presolar silicates have been identified based on in situ measurement, whereas SiCs are chemically separated. The in situ measurements within the meteorite sections have much less of an effect on the morphology of the grains, and hence the amorphous grains remain unaltered/intact. On the other hand, harsh chemicals used in chemical separation method could lead to the destruction of presolar grains, especially amorphous grains (disordered structure) in comparison to crystalline ones (ordered crystals). Limited efforts have been put into an in situ search of SiC within meteorite sections, and no morphological studies exist for them as of yet. Nonetheless, simulation in the present study indicates amorphization of ice-mantle SiC through GCR interactions, and hunting for these amorphous grains through in situ searches in future would be desirable. As the ice thickness or the density increases, the GCR loses more energy and increases the capacity of destruction. Introduction of Si and C from the core in this ice mantle may also increase the density of the ice mantle; however, this


O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O B-Wavelength O O O O O B-Wavelength O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O B-CelestialObject I-CelestialObject O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O B-Wavelength O O O O O O O O O O O B-Instrument B-Wavelength I-Wavelength I-Wavelength O O O B-Archive I-Archive O B-CelestialObject I-CelestialObject O O O B-Survey O O O O O O O O O O B-Wavelength O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O B-Telescope B-Instrument O O O O O B-Instrument B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O B-Telescope B-Instrument O O O O O O O O O O O O O O O O O O B-Instrument B-Wavelength I-Wavelength I-Wavelength O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O B-Wavelength O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O B-Wavelength O O O O O B-Wavelength B-Wavelength O B-Instrument O O B-Instrument O O O B-Wavelength I-Wavelength I-Wavelength O O O O O B-Instrument B-Wavelength O B-Wavelength I-Wavelength I-Wavelength O O O O O B-Instrument O O O B-Wavelength B-Wavelength O B-Wavelength I-Wavelength I-Wavelength O O O O O B-Wavelength O O O O O O O O O O B-CelestialObject I-CelestialObject O B-Wavelength I-Wavelength I-Wavelength O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O B-Wavelength B-Wavelength B-Instrument O B-Instrument O O O O O O O O B-Instrument O O O O B-Instrument B-Wavelength I-Wavelength I-Wavelength O O B-CelestialObject I-CelestialObject O O O O O O O O B-Instrument O O O B-CelestialObject I-CelestialObject O O O B-Software O O O O O O O O O

that ongoing accretion is occurring at such a slow rate that it is not detectable and that we caught H α in emission when the accretion was barely high enough to detect. Despite the evidence for some gas in the disk and its young age, the disk fractional luminosity and low dust mass of T 43 is consistent with what is seen in debris disks. We conclude that T 54 has ended its primordial disk lifetime and is crossing over the bridge to the debris disks stage. The fact that this is a binary system hastens its evolution, allowing us a rare glimpse of this bridge in a young star-forming region. Future observations of this object will help us understand this short-lived stage. Appendix T 54 has a nearby FIR source that contaminates the observed FIR emission (left, Figure 9 ; Matrà et al. 2012 ). Here we show that this unidentified FIR source should have no significant contribution to most of the data that we study in this paper. The unidentified FIR source is 6′′ away from T 54. Assuming it is in Cha I (at 160 pc), it is located 1040 au away from T 54 at a position angle of 196°. To the best of our knowledge, this FIR source does not overlap with previously reported objects. Figure 9. Left: PACS 70 μ m image from the HSA archive with T 54 and a nearby 2MASS source labeled with red triangles (top and lower, respectively). The FIR source identified by Matrà et al. ( 2012 ) is denoted with a black ellipse. Center: Spitzer IRS spectral footprint overlaid on the PACS 70 μ m image. We show the short-low (yellow) and long-low (black) slits as well as the two nods of the short-high observations (red). Right: Herschel PACS spectral footprint (red boxes) corresponding to the [O i ] observations discussed in Section 4.1.4 overlaid on the PACS 70 μ m image. Note that T 54 is in the central spaxel, which was used to extract the spectrum, and the unidentified FIR source is not covered by the central spaxel. Matrà et al. ( 2012 ) find that the unidentified FIR source is not detected in JHK -band photometry, IRAC photometry, or MIPS data taken at 24 μ m. However, it is detected in PACS 70 and 100 μ m data as well as in SPIRE photometry taken at 160, 250, and 350 μ m. The flux of this unidentified FIR source is comparable to or greater than the flux of T 54 at 100 μ m and beyond (Matrà et al. 2012 ). Therefore we show in Figure 8 the fluxes reported by Matrà et al. ( 2012 ) as upper limits since these data include emission from both the T 54 system and the nearby unidentified FIR source. It is unlikely that the unidentified FIR source is contributing to the Spitzer IRS spectra of T 54. As reported by Matrà et al. ( 2012 ), the unidentified FIR source is not detected in NIR, MIR IRAC, or MIPS images. To explore this further, we overlaid the IRS slit positions on a PACS 70 μ m image of T 54 (center panel, Figure 9 ). Low- and high-resolution IRS spectral observations of T 54 are available in CASSIS. In the low-resolution observations (2005 April 24 10:57:08), the


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We thank the referee for an encouraging and incisive report which improved the quality of this paper. We gratefully thank Thierry Foglizzo for fruitful exchanges and the mpi-amrvac development team, in particular Oliver Porth, Rony Keppens and Zakaria Meliani, for useful assistance. We acknowledge the financial support from the UnivEarthS Labex programme of Sorbonne Paris Cité (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). IEM acknowledges financial support from the ENS of Cachan through a contrat doctoral spécifique pour normaliens and from the University Paris 7 Diderot. The numerical simulations were run on the François Arago Centre facilities in Paris 7 and using the HPC resources from GENCI-CINES (Grant c2015047469).


O O O O O B-Person I-Person O O O O B-Database I-Database O B-Person I-Person O O O O O O O O O O O O O B-Database I-Database I-Database I-Database I-Database I-Database I-Database O O O O O O O O B-Organization O B-Grant I-Grant I-Grant O O B-Organization I-Organization B-Grant B-Person O B-Grant B-Person

We would like to thank Kevin France for discussions concerning the MUSCLES database and Sukrit Ranjan for discussions concerning DNA action specta. This work has made use of the MUSCLES M dwarf UV radiation field database. We would also like to acknowledge support from DFG funding ENP KA 3142/1-1 and the Simons Foundation (290357, Kaltenegger and 290360, Sasselov).


O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-CelestialObject I-CelestialObject O O B-Wavelength O O O O B-Telescope B-Wavelength O B-CelestialObject O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O B-CelestialObject I-CelestialObject O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O B-Citation I-Citation O O O O O O O B-Wavelength O B-Wavelength O O B-CelestialObject I-CelestialObject O O O O B-Telescope I-Telescope I-Telescope O B-Telescope O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

can be asymmetric both in position (i.e. different distances from disc centre) and brightness (e.g. Baptista, Harlaftis Steeghs 2000b ; Baptista et al. 2005 ). Aside of the transient spiral structures seen during dwarf nova outbursts, spiral shocks were also observed in nova-like systems – where they presumably are persistent, tidally induced effects in permanently large and hot accretion discs (Baptista Bortoletto 2008 ; Saito et al. 2010 ). V348 Puppis is the optical counterpart of the faint HEAO X-ray source 1H0709-36, identified by Tuohy et al. ( 1990 ) as an eclipsing CV inside the period gap ( P orb = 2.44 h, Baptista et al. 1996b ; Rolfe, Haswell Patterson 2000 ). Its light curve, which shows the gradual eclipse of an extended source, and the observed rotational disturbance in its emission lines during eclipse indicate the presence of a bright, high mass accretion rate disc outshining the contributions from the WD at disc centre and the bright spot at disc rim. The detection as a hard X-ray source, the presence of a strong He ii λ4686 emission line in the spectrum and the possible existence of a second periodicity close to the orbital period led to the suggestion that V348 Pup might be a magnetic CV of the DQ Her type close to synchronize (Tuohy et al. 1990 ; Rosen et al. 1994 ). However, its spectrum exhibits strong single-peaked Balmer and He i emission lines that remain largely unobscured during disc eclipse (indicating significant contribution from above the orbital plane) and displays absorption components at phases opposite to the disc eclipse (φ = 0.4–0.5). This spectroscopic behaviour led Rodríguez-Gil et al. ( 2001 ) to classify V348 Pup as a nova-like variable of the SW Sex type. Moreover, the nature of the second periodicity became clear with the discovery of long-lasting, positive superhumps (with a period 6 per cent longer than P orb ), resulting from the gravitational interaction between a slowly precessing non-axisymmetric accretion disc and the mass-donor star (Rolfe et al. 2000 ). Its eclipsing nature and the location within the period gap make V348 Pup an obvious target for an investigation of its accretion disc properties with eclipse mapping techniques (Horne 1985 ). For this purpose, time series of UV and optical spectroscopy of V348 Pup were collected with the Hubble Space Telescope ( HST ). A first analysis of this data set were reported by Froning, Long Baptista ( 2003 ). They found that the HST out-of-eclipse spectrum is characterized by a blue continuum with strong emission lines and a broad dip in the spectral range λ2000–3000 Å (attributed to a blend of Fe ii absorption lines known as the ‘Fe ii curtain’; Horne et al. 1994 ), but the Balmer jump is shallow or absent. The eclipses are remarkably shallow across the observed spectral range (≃40–50 per cent of the out-of-eclipse light remains visible at mid-eclipse in the continuum, and up to 80 per cent in the emission lines) indicating that a significant


O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O B-Citation I-Citation O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O

that the progenitor was enshrouded in a dusty cocoon of material that was lost close to the explosion. If the SN was not an electron capture SN it would have been the explosion of a 11 M ⊙ red supergiant. However 2008S has little in common with other such SN from progenitors in this mass range (Smartt 2015 ; Davies Beasor 2018 ). In conclusion using the new distance to determine the luminosity of the progenitor we find it more likely than before that SN 2008S was an electron capture event. It also was likely to have been the result of a binary interaction which was suggested by Podsiadlowski et al. ( 2004 ) to be the most likely channel for such core-collapse events. While SN 2008S is at the minimum mass for a core-collapse SNe, N6946-BH1 is at the maximum mass for a core-collapse of a red supergiant. This star was observed to rapidly fade with a light curve that was in agreement with a source powered by a feeding black hole (Adams et al. 2017 ). When the nature of the progenitor was examined this study assumed a distance of 5.95 Mpc. Therefore again this increases the suggested progenitor luminosity from log ( L/L ⊙ ) = 5.3 to 5.5. As shown in Fig. 1 this increase in the luminosity implied a mass for the progenitor star or 24 M ⊙ that is above the predicted mass limit for the formation of a black hole. This is also consistent with the mass estimated from the surrounding stellar population by Murphy et al. ( 2018 ). Again while it is only one event tension between the mass estimates for black hole formation and the luminosity of the observed progenitor stars are reduced by this study. We note that this result is in agreement with the work of Murphy et al. ( 2018 ). 4 CONCLUSIONS We have re-evaluated the distance to NGC 6946. The value of 5.9 Mpc is incorrect and should not be used in future studies. We used the observed SN rate to estimate the star formation rate and thus the FUV luminosity of the galaxy. Using the standard candel method we derive a distance of 7.9 ± 4.0 Mpc. This is consistent with the more recent distances estimated by Anand et al. ( 2018 ) and Murphy et al. ( 2018 ) of 7.72 ± 0.32 Mpc and 7.83 ± 0.29 Mpc, respectively. We strongly recommend that all future studies concerning NGC 6946 use the updated distance of 7.72 ± 0.32 Mpc from Anand et al. ( 2018 ). Their distance is consistent with the distance of Murphy et al. ( 2018 ) but Anand et al. ( 2018 ) took additional steps to reduce contamination and is therefore preferred. We re-evaluated the nature of the five progenitors of observed core collapse events in NGC 6946 using the distance of 7.72 ± 0.32 Mpc. We found that the mass constraints change significantly. The two most significant changes are: first, that the observed progenitor of SN 2008S is now more consistent with predictions for the progenitors of electron capture SNe. We suggest that SN 2008S was an electron capture SN with the progenitor having experienced a binary interaction before explosion. Second, the


O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O B-CelestialObject O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O B-CelestialObjectRegion I-CelestialObjectRegion O O O O O O O O O O O O O O O O O O O B-CelestialObjectRegion O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O B-Survey I-Survey I-Survey I-Survey I-Survey O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObjectRegion O B-Citation I-Citation I-Citation I-Citation O O O O O B-CelestialObjectRegion O O O O O O O O O O B-CelestialObjectRegion I-CelestialObjectRegion O O O O O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O B-Survey I-Survey I-Survey O O O O

the microlensing detection (e.g. Alcock et al. 2000 ), halo white dwarfs have been suggested as natural candidates to contribute to the dark matter content of the Galaxy (e.g. Oppenheimer et al. 2001 ). An intense debate arose on this issue, although later studies demonstrated that the white dwarf contribution to dark matter was rather limited (e.g. Torres et al. 2002 ; Flynn, Holopainen Holmberg 2003 ; García-Berro et al. 2004 ; Kilic et al. 2004 ; Bergeron et al. 2005 ). In any case, the search for white dwarfs in the Galactic halo has proven to be a difficult endeavour. In this sense, the intrinsic faintness and the low space density of halo white dwarfs, along with their high surface gravity, which erases any trace on metal content from their atmospheres and disables accurate radial velocity measurements due to the broadening of the Balmer lines, are some of the main factors that have hindered the discovery of suitable candidates. Consequently, during decades, the identification of halo members has relied on the search of cool objects in high proper motion surveys (e.g. Monet et al. 2000 ; Nelson et al. 2002 ; Hall et al. 2008 ; Catalán et al. 2012 ; Munn et al. 2016 ). It was not until the ESO SNIa Progenitor surveY project (see Napiwotzki et al. 2020 , and references therein) that radial velocities were measured for the first time with enough precision to recover the 3D kinematics of white dwarfs. That permitted to identify high eccentric retrograde orbits as strongly indicators of their belonging to the halo population (Pauli et al. 2006 ). Although the number of halo members was sparse, an estimate of the age of the inner halo has been possible ( Gyr; Kalirai 2012 ). A key ingredient of these studies is the white dwarf luminosity function. Defined as the number of white dwarfs per bolometric magnitude unit and cubic parsec, the white dwarf luminosity function is a valuable tool to derive the age, history, and evolution of the components of our Galaxy. Moreover, the luminosity function holds all the information about the cooling process of the white dwarfs, being then an excellent tool for testing the physics of evolutionary models (see García-Berro Oswalt 2016 , for a comprehensive review about these issues). However, the effectiveness of the white dwarf luminosity function requires the existence of a complete, well-defined volume sample. In this sense, the lack of accurate distances previous to the Gaia era, joint to the selection biases inherited from magnitude-limited samples, have hampered the achievement of more conclusive results in such an elusive sample as the halo white dwarf population. The first observational halo white dwarf luminosity function (Liebert et al. 1989 ) contained only five objects, and no more than 20 were proposed as halo candidates through a neural network artificial intelligent classification algorithm (Torres, García-Berro Isern 1998 ). Based on the SuperCOSMOS Sky Survey observations towards the southern


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We thank Paz Beniamini, Petar Mimica, Enrico Ramirez-Ruiz, Lorenzo Sironi, and Alexander van der Horst for useful comments on the manuscript. We acknowledge support from NASA grant no. NNX13AP13G.


O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

15 Myr. This excess in BH number can be partially explained by an increase in binary interaction rates in these models. Specifically, model 2a has a higher number of binary mergers involving stars with zero-age main sequence (ZAMS) masses between 10 and 25 M ⊙ that would not have otherwise been BH progenitors (at 0.1 Z ⊙ , the minimum ZAMS mass that will form a BH is roughly 20 M ⊙ ). However, these merger products do evolve into BHs with masses roughly in the range of M BH ≈ 5–15 M ⊙ . For models 2e and 2k , the higher number of BHs can be partially attributed to mass transfer in a binary increasing the mass of one of the components past the threshold of BH formation. Naturally, some of these differences are clearly due to stochastic fluctuations in the initial evolution of the model, leading to divergent paths in the dynamical evolution of the system. The main takeaway is that binary evolution processes, coupled with dynamics, can greatly influence BH growth. We leave a detailed study of the extent to which binary evolution processes affect the long-term cluster evolution and dynamics for a future study. It is important to note that many (roughly 55%) of these “excess” BHs formed with masses less than 15 M ⊙ are ejected promptly from their host cluster through natal kicks. Low-mass BHs are expected to form with less mass fallback and thus receive larger natal kicks (e.g., Fryer et al. 2012 ). Thus, this excess of BHs formed is unlikely to have a significant effect on the long-term cluster dynamics. 4. Discussion and Conclusions Our results show that high binary fractions for massive stars lead to an increase in binary-mediated dynamical interactions, which in turn have an important effect on massive BH formation. We have demonstrated that increasing the high-mass binary fraction, consistent with observations, while keeping all other cluster parameters (e.g., cluster masses, virial radii, metallicity) fixed at the values used in Kremer et al. ( 2020b ), may significantly change the early evolution of YMCs. In particular, high-mass binaries facilitate high rates of massive star collisions (occurring through both dynamical encounters and binary-evolution-driven mergers) that can lead to the formation of massive BHs, both within and above the pair-instability mass gap. With the exception of the high-mass binary fraction, the parameters for the models calculated in this Letter are identical to those in Kremer et al. ( 2020b ), which were shown to lead to present-day properties matching well those of Milky Way GCs. If indeed the majority of high-mass stars have binary companions at birth, massive BH formation may therefore be a common occurrence in the early phases of GC evolution. As shown in Figure 2 , the formation of massive BHs is sensitive to small changes in initial virial radius. This is in agreement with previous works on the topic of IMBH formation that have shown that the onset of a collisional runaway occurs abruptly under small


O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O B-Observatory B-Telescope B-Citation I-Citation I-Citation I-Citation I-Citation O B-Telescope B-Citation I-Citation I-Citation I-Citation O O B-Telescope B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O B-CelestialObject I-CelestialObject O O O O O O O O O B-Model O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O B-Model B-Citation I-Citation I-Citation I-Citation O O O O O O B-Model O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O

index Γ and the inner disc temperature are consistent with the results of previous studies of M33 X-8, where a similar spectral model and data from Swift /XRT (La Parola et al. 2015 ), XMM–Newton (Foschini et al. 2004 ), or Suzaku (Isobe et al. 2012 ) were used. The innermost disc radius, R in , can be directly estimated from the normalization of the diskbb component: , where D is the distance to the source in units of 10 kpc and i is the inclination of the disc. The estimated inner disc radius, R in = (37 ± 2)cos −1/2 i km, is in good agreement with the results of previous studies (e.g. Middleton et al. 2011 ). Associating this size with the radius of the innermost stable orbit of a standard accretion disc suggests that the relativistic compact object has a mass of at least ∼4 M ⊙ , with the exact value depending on the (unknown) inclination of the disc. More accurate estimation should take into account the inner boundary condition, the spectral hardening and relativistic corrections, which in turn would depend on the structure of the accretion disc (whether it is thin or slim). Nevertheless, the above crude estimate is consistent with the compact object being a stellar-mass black hole. Replacing the power-law component by its modification with an exponential cut-off (Model 5) further improves the fit statistics to χ 2 /d.o.f. =891/900, indicating the presence of a high-energy cut-off in the spectrum (the F -test probability is 10 −14 for the null-hypothesis Model 4). We conclude that the broad-band 0.3–20 keV spectrum of M33 X-8 cannot be described by a single accretion disc model diskpbb , which was previously used to successfully fit some narrow-band spectra of this source (e.g. La Parola et al. 2015 ). The broad-band spectrum strongly requires an additional power-law component with a possible high-energy cut-off. 3.3 Physically motivated models We have demonstrated that the broad-band spectrum of M33 X-8 certainly contains two components: the first one is well approximated by a multicolour disc with the inner temperature of kT ∼ 1 keV, and the second one is a power-law-like high-energy tail detected up to 20 keV. As often discussed in the literature (e.g. Gierliński et al. 1999 ; Steiner et al. 2009 ), the combination of a low-energy blackbody-like component with a high-energy power law does not allow one to properly model the spectrum at low energies, because a steep power law extending to the soft part of the spectrum requires the introduction of an artificially high absorption column density and can result in erroneous determination of the disc properties. This problem can be solved by using a self-consistent Comptonization model that has a low-energy cut-off in the otherwise power-law-like spectrum, such as the convolution model simpl (Steiner et al. 2009 ), which provides a description of Comptonization based on the non-relativistic theory developed by Sunyaev Titarchuk ( 1980 ). In this model, a fraction of the photons from an


O O O O B-Telescope O O O O B-Telescope O O O O B-Model I-Model I-Model O O O O O O O O O O B-Model I-Model O B-Citation I-Citation O O O O O O O B-Model I-Model O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O B-Telescope O O O O O B-Wavelength I-Wavelength O B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O B-Wavelength O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O B-ObservationalTechniques I-ObservationalTechniques O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O B-Wavelength I-Wavelength O O O O O O B-Telescope O O O O B-Person I-Person O O O O O O O O O O O O O O O O O O O B-ObservationalTechniques O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O

images are for the HST bands and for the Spitzer bands. We adopt a -CDM cosmological model with km s Mpc, , and . We assume a Salpeter IMF ( Salpeter 1955 ). All magnitudes are expressed in the AB system ( Oke Gunn 1983 ). 2. Data 2.1. Spectroscopy The available low-resolution (LR, ) and medium-resolution (MR, ) VLT/VIMOS spectroscopy covering the spectral ranges 3400–7000 Å and 4800–10 000 Å were obtained during 2005, with 4hr exposure time for both LR and MR spectra. The LR spectrum continuum sensitivity is at 3700 Å with 4 h and assuming seeing and airmass 1.2. It is calculated over one pixel along dispersion and (full width half maximum) along spatial direction. ( Popesso et al. 2009 ; Balestra et al. 2010 ). Slit widths of were adopted and the median seeing during observations was . We have newly reduced both configurations, in particular focusing on the Lyman continuum emission (LR-spectrum) and the ultraviolet spectral properties in the non-ionizing domain (MR-spectrum). Reduction was done in two ways: as described in Balestra et al. (2010) and the AB–BA method as described in Vanzella et al. (2011 , 2014b) . Both methods produce consistent results. Recently, a near infrared spectrum of Ion2 was obtained with Keck/MOSFIRE in March 2015 (PI: Günther Hasinger). Integration time of 32, 32, and 36 min were obtained in the -, -, and -bands, respectively, with the AB–BA dithering pattern of 2.9. The adopted slit width was 0.7 producing a dispersion of 1.30 Å, 1.63 Å, and 2.17 Å per pixel, in the -, -, and -bands, respectively; the pixels scale along the spatial direction was 0.18/pixel. Ion2 was inserted in a mask aimed to target low- objects as well. The -band is useful for monitoring low- emission lines. Reduction was performed using the standard pipeline 1 . Briefly, two-dimensional sky-subtracted spectra, rectified and wavelength calibrated, are produced from which the one-dimensional variance weighted spectrum is extracted with a top-hat aperture. The wavelength solution was computed from sky emission lines (e.g., Rousselot et al. 2000 ) in the three bands reaching an rms accuracy better than 1/20, 1/30, and 1/40 of the pixel size in -, -, and -bands, respectively (typical rms 0.05 Å). Table 1 Emission line properties. Notes. (a) Observed emission line flux and error corrected for slit losses (50%) in units of erg s cm. In parenthesis, the [O iii ] flux adopting the theoretical ratio ( Storey Zeippen 2000 ). (b) The emission line dust correction method is described in Appendix A . (c) FWHM (instrumental corrected) and error in units of km s. (d) Equivalent width and error in units of Å. (e) Sum of the two components. (f) Main component. (g) Marginal detections (Fig. 6 ): , , and . (h) FWHM is the contribution of the two blended components, 1907–1909 Å. (i) The error is large because the line is on the top of a sky line (Fig. 4 ). Flux calibration was performed by observing the standard star A0V HIP 26577. Given the slit width () and the


O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O B-Survey O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O B-Survey O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O B-CelestialObject I-CelestialObject O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O B-Survey O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O B-Survey O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O B-Wavelength O B-Wavelength O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject O B-CelestialObject I-CelestialObject O O O O O O O O O O O B-Survey O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation B-Citation I-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O B-Wavelength O O O O O O O O O O O O O O B-Wavelength O O O O O O B-CelestialObject O O O O O O B-Wavelength O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O O O O O O O

to calculate N H values for all targets studied. For 1ES 0229+200, the calculated value of N is (13.00 ± 0.37) × 10 20 cm −2 . This value is larger than the one from the LAB survey (8.06 × 10 20 cm −2 ) and consistent with the one provided by Willingale et al. ( 2013 ,10.80 × 10 20 cm −2 ). The value is also higher than free N H = (10.6–10.8) × 10 20 cm −2 , calculated by Kaufmann et al. ( 2011 ). For PKS 0548−322, the calculated value of N is (3.10 ± 0.10) × 10 20 cm −2 . This value is larger than the one from the LAB survey (2.58 × 10 20 cm −2 ) and consistent with the one provided by Willingale et al. ( 2013 , 2.87 × 10 20 cm −2 ). However, Sambruna Mushotzky ( 1998 ) have found a significantly higher value of N H of 1.03 × 10 21 cm −2 , which is needed to explain X-ray properties of PKS 0548−322. For 1ES 1741+196, the calculated value of N is (10.47 ± 0.41) × 10 20 cm −2 . This value is larger than the one from the LAB survey (7.32 × 10 20 cm −2 ) and consistent with the one provided by Willingale et al. ( 2013 , 9.58 × 10 20 cm −2 ). For 1ES 2344+514, the calculated value of N is (17.34 ± 0.15) × 10 20 cm −2 . This value is larger than the one from the LAB survey (15.10 × 10 20 cm −2 ); however, it is smaller than the one provided by Willingale et al. ( 2013 , 24.60 × 10 20 cm −2 ). We note here that the reddening E ( B − V ) and the atomic hydrogen column density ( N H ) are related. According to recent work, Liszt ( 2014 ) has described this dependence by the following formula N H = 8.3 × 10 21 E ( B − V ). The formula gives N H values of 9.7 × 10 20 , 2.5 × 10 20 , 0.6 × 10 20 , 6.3 × 10 20 , and 15 × 10 20 for 1ES 0229+200, PKS 0548−322, RX J 1136+6737, 1ES 1741+196, and 1ES 2344+514, respectively. The quoted values are consistent with the ones from the LAB survey and do not indicate a need for an additional absorption. All values of N H values, including the catalogue ones, are collected in Table 5 . Table 5. Summary of Galactic column densities values. Notes . (1) Source name; (2)–(4) N H as provided by Kalberla et al. ( 2005 ), Dickey Lockman ( 1990 ), and Willingale et al. ( 2013 ), respectively; (6) N H value calculated as a result of this work. All values are given in 10 20 cm −2 . 4.2 Constrains on the model parameters The model used to describe the IR to X-ray emission of the blazars is characterized by the host galaxy, curvature seen in the X-ray spectrum, total absorption (which includes both Galactic component and possibly additional ones), and UV excess. The host galaxy, understood as the entire component described with the template by Silva ( 1999 ), is well constrained with the model used. Still, the remaining three parameters cannot be disentangled only using information from the X-ray spectral fitting. The limitations on three entangled parameters are as follows: β : For all of the blazars studied, the convex curvature of the X-ray spectrum is assumed. This implies that negative values of β are not accepted.


O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O B-Survey O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-Software O B-Software O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O B-Software O B-Software O O O O O O O O O O O O O O O O O O O O O O O O O O O

between 10 10 and 10 11 M ⊙ . McCarthy et al. ( 2020 ) also use an analytic model, but paired with SDSS observations to explore the host galaxy mass function along with other host observables. For the host galaxy mass function, our results are consistent with theirs. However, our larger range of DTDs presented in Figure 2 reveals the large spread between different assumed DTDs and the stable peak near 10 10.5 M ⊙ . Adhikari et al. ( 2020 ) also find that other host observables paired with stellar mass are necessary to obtain a better understanding where BNSs merge. Overall, we find that future explorations of this topic will need to consider a wide range of DTDs and the full range of the observable in question. While the work we present here continues our understanding of what we can learn from observations of BNS host galaxies, further investigations are necessary to fully understand how BNSs form and evolve. One example of such an investigation is to expand the set of DTDs examined using the methods in this paper. The set of DTDs we examine is broad, covering those most commonly referenced (e.g., Eldridge Stanway 2016 ; Safarzadeh Berger 2019 ), but we do not exhaustively search the full range of DTDs proposed (e.g., Dominik et al. 2012 ; Simonetti et al. 2019 ). Also, our convolution of IllustrisTNG’s SFRH with our DTDs does not include any form of natal kicks. If these kicks are strong enough to dislodge the binary from smaller galaxies, it is possible that their addition would weight the host mass functions toward higher-mass galaxies. With a greater range of DTDs examined and a more detailed convolution, we will gain a clearer picture of where BNS mergers are located, which delay times can be distinguished using the host galaxy mass function, and the most likely places they will be observed. Another way to incorporate a more complete set of DTDs would be to use a varied set of population synthesis models that cover a wide range of binary separations, kick velocities, initial mass functions, etc. Including other star formation histories could also provide a more detailed look at the spread in possible host galaxy mass functions. While IllustrisTNG is broadly consistent with the cosmic SFR density and redshift-dependent galaxy stellar mass functions (Pillepich et al. 2018a ), its accuracy should not be overinterpreted, and different simulations will surely produce somewhat varied star formation histories that could impact our results. However, we can say that up to their mass cutoff our results align with those of Artale et al. ( 2019 ), who found no significant difference when comparing results from Illustris and Eagle. The lack of variation in Artale et al. ( 2019 ) most likely indicates that—while there is some variation—the SFRHs in Illustris and EAGLE are sufficiently similar to not significantly impact the results. Thus, by adopting the SFRHs from galaxy formation simulations and assumptions about the functional form of the DTD,


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ACKNOWLEDGEMENTS Our research was supported by the Joint Research Fund in Astronomy (No.11963002; U1631236 and U1431114) under a cooperative agreement between NSFC and CAS. We also want to thank Dr Frank Levinson for his generous financial support that enabled Butler University to join the SARA telescope consortium and upgrade its Holcomb Observatory telescope. This work was also supported by the Natural Science Foundation of Guizhou Province Office of Education (Grant No. 2014298). We also thank Professor Prabhakar Misra for revising the language of our paper. We acknowledge the support of the staff of the Xinglong 60-cm telescope and Cultivation Project for LAMOST Scientific Payoff and Research Achievement of CAMS–CAS.


O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation B-Citation I-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O O O O O O O O O O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

by magenta, green, and orange lines, respectively, with solid (dashed) lines indicating results for the northern (southern) hemisphere. The SSN is shown for each hemisphere. 6. Discussion Taken at face value, the results as illustrated by Figures 10 and 11 are unexpected in that the shallow return flow present in the northern hemisphere appears to be inconsistent with most prior determinations of the meridional circulation that employ multiyear observations and attempt to remove the effects of center-to-limb related artifacts. Specifically, most analyses involving modeling time–distance travel-time perturbations show a poleward flow in both hemispheres that persists from the surface down to approximately 0.9 R ⊙ (i.e., about 70 Mm below the surface). This includes the analyses of Zhao et al. ( 2013 ), Jackiewicz et al. ( 2015 ), Rajaguru Antia ( 2015 ), and Chen Zhao ( 2017 ). A notable exception is the recent analysis of Gizon et al. ( 2020 ), which is discussed below. In general, uncertainties in the inference of the flow increase with the depth of those inferences. This makes the discrepancy with other helioseismic analyses at a relatively shallow depth all the more puzzling. If we assume that the results for at least the northern hemisphere are spurious, then the challenge is to understand the cause of what appears to be an uncorrected artifact. Of course, real hemispheric differences in the meridional circulation may very well exist, but it is worth considering the possible nature of pseudoflows, which are themselves asymmetric. The comparison of the time variation of the frequency shifts with the sunspot numbers for both hemispheres (Figure 12 ) indicates that the observed hemispheric differences in the 88 month interval persist regardless of the level of solar activity or its preference for one hemisphere over the other. While this does not rule out the presence of real solar-cycle variations in flows (e.g., Chou Dai 2001 ; Zhao Kosovichev 2004 ; González Hernández et al. 2008 ; Hathaway Rightmire 2010 ) or potential pseudoflow artifacts related to magnetic regions (e.g., Liang Chou 2015 ), there is no direct correlation between hemispheric differences in solar activity and the differences in the frequency shifts. Errors in the control measurements due to uncertainties of the leakage discussed in Appendix B appear to be too small to account for the hemispheric differences observed in Figure 9 . In particular, we note that likely errors in the leakage factor amounting to 20% of the selected value of 0.84 (see Appendix B ) cause uncertainties in the scaled frequency shifts of the deepest modes of around 1 m s −1 . These are smaller than the standard errors of the observations shown in Figure 9 and substantially smaller than the 4 m s −1 discrepancy observed at the highest phase speeds. It is plausible that the results may be compromised by incorrect assumptions regarding the azimuthal invariance of the center-to-limb correction. At


B-Person O B-Organization O O O O O B-Organization I-Organization I-Organization O O B-Person O B-Organization I-Organization O O O O B-Organization I-Organization I-Organization O O O O O O B-Organization I-Organization O O O O B-Fellowship I-Fellowship I-Fellowship I-Fellowship B-Person O B-Person O O B-Organization I-Organization I-Organization O O O

SLS thanks STFC for her studentship and the Australian National University for hospitality. CAT thanks Churchill College for his fellowship, the Australian National University for a visiting fellowship and the Monash University for support as a Kelvin Watford distinguished visitor. LF and DTW thank the Institute of Astronomy for supporting visits.


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This work was supported by the European Research Council under ERC grant agreement no. 337705 (CHASM) and by a Consolidated Grant from the UK STFC (ST/J001627/1). Some of the calculations for this paper were performed on the DiRAC Complexity machine, jointly funded by STFC and the Large Facilities Capital Fund of BIS, and the University of Exeter supercomputer, a DiRAC Facility jointly funded by STFC, the Large Facilities Capital Fund of BIS, and the University of Exeter. We thank Isabelle Baraffe for providing the 1D stellar structure model used in this paper and for offering comments on an earlier version of this manuscript. We also thank the referee for a thorough reading of our paper and providing many helpful comments, improving the clarity of our paper.


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Acknowledgements We thank the referee for useful suggestions; Sebastian Hönig for many illuminating discussions; Claudio Ricci for careful reading and comments on the manuscript. MS acknowledges support by the Ministry of Education, Science and Technological Development of the Republic of Serbia through the projects Astrophysical Spectroscopy of Extragalactic Objects (176001) and Gravitation and the Large Scale Structure of the Universe (176003); by FONDECYT through grant no. 3140518; by the Center of Excellence in Astrophysics and Associated Technologies. This research made use of Astropy, a community-developed core python package for Astronomy (Astropy Collaboration et al. 2013 ). Based on European Southern Observatory (ESO) observing programmes 60.A-9629, 076.B-0599, 078.B-0255, 087.B-0746, 088.B-0159, 089.B-0070, 385.B-0896 and 386.B-0026.


O O O B-Person I-Person O B-Person I-Person O O O B-CelestialObject O O B-Telescope I-Telescope I-Telescope I-Telescope O O O O B-Location I-Location I-Location I-Location O O B-Organization I-Organization I-Organization I-Organization I-Organization I-Organization I-Organization O O B-Location B-Observatory I-Observatory I-Observatory I-Observatory I-Observatory I-Observatory O O B-Organization I-Organization I-Organization I-Organization I-Organization O O O O O O O O O B-ComputingFacility I-ComputingFacility I-ComputingFacility I-ComputingFacility I-ComputingFacility B-ComputingFacility O O B-ComputingFacility I-ComputingFacility I-ComputingFacility I-ComputingFacility I-ComputingFacility O B-Organization I-Organization O O B-ComputingFacility I-ComputingFacility I-ComputingFacility I-ComputingFacility I-ComputingFacility I-ComputingFacility B-ComputingFacility O O B-Organization I-Organization I-Organization I-Organization O B-Location B-Person O O O O O O B-Location B-Organization I-Organization B-Grant O B-Location B-Organization I-Organization I-Organization B-Grant O O B-Organization I-Organization I-Organization I-Organization B-Organization O O O O O O B-Grant O B-Grant O O O B-Organization I-Organization I-Organization I-Organization I-Organization O O O B-Organization I-Organization O B-Location O O O B-Grant I-Grant I-Grant O O O O O O O O B-Grant I-Grant I-Grant

Acknowledgements We thank David Bühler and Jayant Joshi for acquiring the quiet-Sun data. The Swedish 1-m Solar Telescope is operated on the island of La Palma by the Institute for Solar Physics of Stockholm University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The computations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at the High Performance Computing Center North at Umeå University and the PDC Centre for High Performance Computing (PDC-HPC) at the Royal Institute of Technology in Stockholm. JdlCR is supported by grants from the Swedish Research Council (2015-03994), the Swedish National Space Board (128/15) and the Swedish Civil Contingencies Agency (MSB). This research was supported by the CHROMOBS and CHROMATIC grants of the Knut och Alice Wallenberg foundation and by the Research Council of Norway through the grant “Solar Atmospheric Modelling” and through grants of computing time from the Programme for Supercomputing.


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ACKNOWLEDGEMENTS SJC would like to acknowledge the support of the Lau Endowment as part of the Undergraduate Research Scholars Program of the UCLA Undergraduate Research Center – Sciences, the Undergraduate Research Fellows Program, and the Maggie Gilbert Research Award through UCLA College Honors. SN thanks Howard and Astrid Preston for their generous support. We would like to thank Professor Stassun, Professor Gómez Maqueo Chew, Professor Heller, and Dr Hamers for their thoughtful comments and suggestions.


O O O O O O O O O O O O O O O B-Model I-Model B-Model B-Citation I-Citation I-Citation I-Citation O O O O B-Model O O O B-Software I-Software O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O B-CelestialObject I-CelestialObject O O O B-Model I-Model O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model O O B-Model O O O B-Software O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

or less blended and we saw only one to three components. Next, we used the least-squares deconvolution (LSD; Donati et al. 1997 ) technique and calculated LSD profiles with the LSD code by Tkachenko et al. ( 2013 ), based on the same line mask as we used for our previously mentioned synthetic spectrum. Figure 1 shows the LSD profiles vertically arranged according to the JD of observation. The resolution is distinctly better than that of the CCFs; four components are now seen in the majority of the LSD profiles. The measured RVs are marked, and the calculated orbital curves plotted in Figure 1 show that we could assign all components in all LSD profiles to four different stars located in two different binary systems, S 1,2 and S 3,4 . Figure 1. LSD profiles calculated from the 29 spectra, vertically arranged according to the JD (2,457,000+) of observation. Measured RVs are marked by open circles and crosses, in the left panel for components C 1 and C 2 and in the right panel for C 3 and C 4 , respectively. The red and green curves illustrate the corresponding, calculated orbital solutions. The RVs of the four components, C 1 to C 4 , were determined by fitting the LSD profiles with multiple Gaussians. The mean (internal) errors of the fit were 0.25, 0.36, 0.28, and 0.37 km s −1 for the RVs of C 1 to C 4 , respectively. We used the method of differential corrections (Schlesinger 1910 ) to determine the orbits from the RVs. Because of the short time span of the observations, this could be done for the two systems separately, without accounting for any interaction between them or for light-travel-time effects. In the case of S 1,2 , we fixed the orbital period to the value known from the Kepler light-curve analysis. The RVs of the four components of KIC 7177553 determined from the multi-Gaussian fit to the LSD profiles are listed in Table 5 in Appendix B . Figure 2 shows the RVs and orbital curves folded with the orbital periods. Table 1 lists the derived orbital parameters. The times of observation of all spectra are based on UTC. To be consistent with the Kepler DCT time scale and the results listed in Table 3 , we added 68 s to the calculated times of periastron passage T . Figure 2. RVs and calculated orbital curves folded with the orbital periods. Left: C 1 (open circles) and C 2 (open squares). Right: C 3 (open circles) and C 4 (open squares). Phase zero corresponds to the time of periastron passage. Table 1 Orbital Solutions Obtained from Multi-Gaussian Fits of the LSD Profiles and with KOREL Note. The table lists period P and orbital elements (eccentricity e , argument of periastron ω , time of periastron passage T , and mass ratio q ) of the two systems, and the RV semiamplitudes K and individual systemic velocities γ . Errors are given in units of the last two digits in parentheses. The last two rows list the rms of the residuals after subtracting the orbital solution from the RVs and the projected masses calculated from the spectroscopic


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The work of R. B. is supported by the Deutsche Forschungsgemeinschaft (DFG) under grant BU 3115/2-1. We thank R. J. MacDowall for providing the Wind/WAVES data and acknowledge the use of the Wind/3DP data. Work at JPL was supported by NASA. Work at APL ( ACE /ULEIS and STEREO /SIT) was supported by NASA grant NNX13AR20G/115828 and NASA subcontract SA4889-26309 from the University of California Berkeley.


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We thank I. Smail for his detailed comments and suggestions that help improve this manuscript; J. M. Simpson for providing the SCUBA2 data; C. Y. Peng and G. Barro for their advice on GALFIT ; S. Zibetti for his support with ADAPTSMOOTH ; C. M. Casey for providing the DSFG comparison data plotted in Figure 4 ; and D. Watson, J. Hjorth, I. Davidzon, H. Rhodin, K. K. Knudsen, P. Laursen, D. B. Sanders, M. P. Haynes, R. Pavesi, T. K. D. Leung, and S. Martín-Álvarez for helpful comments and suggestions. We are grateful to the anonymous referee, whose comments have been very useful to improving our work. C.G.G. and S.T. acknowledge support from the European Research Council (ERC) Consolidator Grant funding scheme (project ConTExt, grant number 648179). A.K., E.J.A., and F.B. acknowledge support by the Collaborative Research Centre 956, subproject A1, funded by the Deutsche Forschungsgemeinschaft (DFG). Support for B.M. was provided by the DFG priority program 1573, “The physics of the interstellar medium.” D.R. acknowledges support from the National Science Foundation under grant number AST-1614213. V.S. acknowledges support from the European Union’s Seventh Framework program under grant agreement 337595 (ERC Starting Grant, “CoSMass”). M.A. acknowledges partial support from FONDECYT through grant 1140099. ERD also acknowledge support by the Collaborative Research Centre 956, subproject C4, funded by the DFG. M.J.M. acknowledges the support of the National Science Centre, Poland, through POLONEZ grant 2015/19/P/ST9/04010; this project has received funding from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement No. 665778. Based on observations made with the NASA/ESA Hubble Space Telescope , obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #13294. Support for program #13294 was provided by NASA through a grant from the Space Telescope Science Institute. This research made use of the following ALMA data: ADS/JAO.ALMA#2012.1.00978.S. ALMA is a partnership of the ESO (representing its member states), NSF (USA), and NINS (Japan), together with the NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by the ESO, AUI/NRAO, and NAOJ. This paper employed Astropy , a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013 ); APLpy , an open-source plotting package for Python (Robitaille Bressert 2012 ); CASA (McMullin et al. 2007 ); Matplotlib (Hunter 2007 ); Numpy ; Photutils (Bradley et al. 2016 ); PyBDSF ; and R, a language and environment for statistical computing.


O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O B-Software I-Software O O O O O O O O O O O B-Software O O O O O O O O O O B-URL O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Software O O O O O O O O O O O O O O O B-Software I-Software I-Software O B-Software I-Software I-Software O B-Software I-Software I-Software O O O O O O O O O O O O O O O O O O O O O O B-Software O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O B-Software O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O B-Organization I-Organization O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Software O O O O O O O O O B-Software O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Software I-Software O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Software O O O O B-Model I-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Software O O O O O O

This completes the presentation of the Galaxy model potential. Appendix C Implementation Notes In this section, we sketch a brief technical resume of the GalMod platform contents (ver. 16.2). Nevertheless, we warn the reader that the platform “GalMod” is continuously updated and the Web page (the tutorial page: www.galmod.org/gal/tutorial ) is the most up-to-date place to search for the latest refinements, bug corrections, and tested implementations that might differ from what is presented in this section. A cycle of 12 upgrades per year is planned. We organized GalMod in modules, i.e., independent sub-units of the source code that interact through interfaces (e.g., the Poisson solver modules, the CMD generator modules, the extinction integrator modules, and so forth). This approach facilitates the use of multiple language codes/libraries with different types of licenses. A rough scheme of the GalMod infrastructure is shown in Figure 17 . We presented each of these modules in dedicated papers. The technique to generate the photometry and chemistry of the stars is introduced in Pasetto et al. ( 2012b ) and references therein, the kinematics and potential solver in Pasetto et al. ( 2016b ) and references therein, and the extinction based on DART-Ray in Natale et al. ( 2017a ). The Web-interface system and cloud computing service is realized and maintained by Clover-lab TM . These references collect the results of several years of work performed by several researchers and programmers. They are not meant to be an exhaustive list. Figure 17. The superstructure of GalMod. Each square box represents a series of modules of GalMod where some computation is performed (either in serial or parallel mode). The numbered blue arrows represent the ideal flux from the input parameters to the delivery of the mock catalog (or the output) . The modules are the Poisson-solver modules that, once the density/potential parameters have been adopted, provide Φ, its gradients and Laplacian, and a series of kinematics indicators (rotation curve, total mass, etc.) relative to . are the modules computing the maximum number of stars for the galaxy considering and the input parameters . can be simply an input parameter depending on the type of simulation. M are the modules assigning the star-like particle mass in the case GalMod is used to generate N -body i.c.. N is the number of stars generated so far. are the modules distributing the stars according to the density profiles, , their number N , and the input condition . The age/metallicity/velocity dispersion modules compute the distribution of the stars or star-like particles in the age τ , metallicity Z , and velocity space. They include the mass generation of the star and the extinction modules in the case of mock stellar catalogs only, while a separate module provides the same information with a preassigned stellar particle mass in the case of i.c. generation. GalMod produces a stochastic realization (i.e., stellar


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This work was supported in part by the Collaborative Research Center TR 33 “The Dark Universe” of the Deutsche Forschungsgemeinschaft. This work is based on data collected at the ESO VLT (prog. ID 186.A-0798).


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M.Š. acknowledges the support of the Czech Science Foundation (grant 14-04338S) and of the institute research project RVO:67985815 to Astronomical Institute of Czech Academy of Sciences. A.S.B. acknowledges financial support by CNES Solar Orbiter grant, CNRS/INSU Programme National Soleil-Terre, ERC STARS2 207430 and SolarPredict 640997 grants and wishes to thank M. DeRosa for useful discussions.


O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O B-Wavelength O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model I-Model B-Model B-Citation I-Citation O B-Citation O O O O O O O O O O B-Model I-Model I-Model I-Model I-Model B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation O B-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation O B-Citation O B-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation B-Citation I-Citation I-Citation I-Citation I-Citation B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O B-Model I-Model I-Model I-Model I-Model B-Model B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O

by Werner, Rauch Kruk ( 2018 ) in the hot white dwarf in the peculiar binary nucleus of the planetary nebula EGB 6. Ar vii λ = 1065.55 spectral line is observed in ultraviolet spectra of hot PG 1159 and extremely hot helium rich white dwarfs (Werner, Rauch Kruk 2016 , 2017 ). Ar iii and Ar ii spectral lines are used in the determination of argon abundance in B-type star and subdwarf atmospheres (Heber Edelmann 2004 ; Blanchette et al. 2008 ; Lanz et al. 2008 ; Fossati et al. 2009 ). In our recent works, Hamdi et al. ( 2017 ) and Hamdi et al. ( 2018 ), we have reported Stark widths for 300 spectral lines of singly charged argon (Ar ii ). Our Stark widths were compared with experimental results and good agreements were found for most spectral lines. In order to complete the set of Stark broadening parameters of Ar ii spectral lines, we report here Stark shifts. Stark shifts are calculated using semiclassical perturbation approach (SCP) (Sahal-Bréchot 1969a , b ) and a set of atomic data is calculated using Hartree–Fock method with relativistic corrections (Cowan 1981 ). Our results are compared with experimental results for 100 spectral lines. Shifts by collisions with ionic perturbers are also taken into account. We also present results as a function of temperature for 161 spectral lines for collisions with electrons, protons, singly charged helium, and singly charged argon. In previous works (Hamdi et al. 2011 , 2013 , 2014 ), the same method was used and we have determined Stark broadening parameters for 114 spectral lines of Pb IV and 32 spectral lines of Ar iii . 2 THE IMPACT SEMICLASSICAL PERTURBATION METHOD A detailed description of this formalism with all the innovations is given in Sahal-Bréchot ( 1969a , b , 1974 , 1991 ), Fleurier, Sahal-Bréchot Chapelle ( 1977 ), Dimitrijević, Sahal-Bréchot Bommier ( 1991 ), Dimitrijević Sahal-Bréchot ( 1996 ), Sahal-Bréchot, Dimitrijević Ben Nessib ( 2014 ), and earlier papers. The profile F (ω) is Lorentzian for isolated lines: where i and f denote the initial and final states and E i and E f their corresponding energies and w is the half width. The shift ( d ) (in angular frequency units) of an electron-impact shifted spectral line can be expressed as: where N is the electron density, the Maxwellian velocity distribution function for electrons, denotes the impact parameter of the incoming electron. The phase shift due to the polarization potential ( r −4 ), is given in section 3 of chapter 2 in Sahal-Bréchot ( 1969a ) and R D is the Debye radius. The cut-off R 3 is described in section 1 of chapter 3 in Sahal-Bréchot ( 1969b ). Energy levels and oscillator strengths needed for SCP calculations of Stark shifts are obtained using Hartree–Fock method with relativistic corrections (HFR) (Cowan 1981 ). We use as for the width calculations an atomic model including 24 configurations: 3s 2 3p 5 ; 3s 2 3p 4 nl ( nl = 4p, 4f, 5p, 5f, 6p, 6f, 6h, 7p, 7f, 7h) (odd parity) and 3s 3p 6 ; 3s 2 3p 4 n ′ l ′ ( n


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The authors would like to acknowledge Rainer Beck for helpful discussions. J.T.L. and J.N.B. acknowledge the financial support from NASA through grants NNX15AM93G, NAS2-97001, 80NSSC18K0536, and GO7-18073X.


O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O B-Citation O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Instrument O O O O O O O O O O O O O O O O O O O O O O O O O B-Observatory I-Observatory I-Observatory B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O B-Instrument O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O B-Citation B-Citation I-Citation I-Citation I-Citation O O B-Telescope B-Citation I-Citation I-Citation I-Citation O

the two objects could also exhaust helium shell burning and simply cool into double degenerates. Upon merger, they would likely form a rapidly rotating CO WD, potentially preceded by an R CrB phase if substantial He remains, as expected for hybrid WDs (Perets et al. 2019 ). For further details on these systems, please see Kupfer et al. ( 2020a , 2020b ). 6. Conclusion Using data from the ZTF, we have significantly increased the number of known binary systems with an orbital period of less than one hour. Using high-speed photometric follow-up in combination with spectroscopic follow-up, we have characterized the physical parameters of the systems using model-dependent techniques invoking WD mass–radius relations. In future work, we hope to obtain more model-independent measurements such as orbital decay rates to more robustly characterize the physical parameters of these systems. We will continue to analyze ZTF data as it accumulates more epochs and discovers more such objects. At the current stage of the survey, the sample we have discovered exhibits a remarkably high fraction of pairs of He WDs, likely due to selection effects. As we continue the survey, we anticipate discovering more systems and that our discoveries will begin to include other classes of sources, such as pairs of CO WDs. All of the detached systems in our sample should be undergoing rapid orbital decay due to general relativity, and we expect to detect this orbital decay in every detached system with high significance before LISA launches. The algorithms and analysis techniques we are developing will be applicable to upcoming surveys such as the one that will be conducted by the Vera Rubin Observatory (LSST Science Collaboration et al. 2009 ). These data sets will be accompanied by their own challenges (in particular, lower cadence, split across many filters). Given the clear promise demonstrated by the discoveries emerging from ZTF, we are optimistic that optical time-domain surveys will continue to revolutionize our understanding of binaries in the millihertz regime. These surveys will set the stage for LISA, having discovered dozens, if not hundreds, of sources by the time the instrument begins to operate (Korol et al. 2017 ). In future work, we will characterize our recovery efficiency in greater detail using synthetic lightcurves, in order to better characterize ZTF’s sensitivity to detecting the population of DWDs in the galaxy. Efforts are currently underway to increase sensitivity to the shortest-period binary systems by accounting for their orbital period evolution, which requires algorithms that can accommodate acceleration searches (Katz et al. 2020 ). Binaries with compact object components are transitioning into a golden age, as we enter an era when time-domain surveys such as ZTF enable detection via periodic features. Massively multiplexed spectroscopic surveys acquiring multiple epochs such as SDSS-V (Kollmeier et al. 2017 ) and LAMOST (Cui et al. 2012 )