adsabs/FOCAL huggingface dataset:
In recent years, numerous low-mass and ELM WDs have been detected in the context of relevant surveys, such as the SDSS, ELM, SPY and WASP (see, e.g., Koester et al. 2009; Brown et al. 2010, 2016, 2020; Kilic et al. 2011, 2012; Gianninas et al. 2015; Kosakowski et al. 2020). The discovery of their probable precursors, namely, the so-called low-mass pre-WDs, has triggered an interest in these types of objects because of the possibility of studying the evolution of the progenitors that lead to the WD phase. Even more interestingly, the detection of multi-periodic brightness variations in low-mass WDs (Hermes et al. 2012, 2013a,b; Kilic et al. 2015, 2018; Bell et al. 2017, 2018; Pelisoli et al. 2018), and low-mass pre-WDs (Maxted et al. 2013, 2014; Gianninas et al. 2016; Wang et al. 2020) has brought about new classes of pulsating stars known as ELMVs and pre-ELMVs, respectively (ELM and pre-ELM variables, respectively). It has allowed for the study of their stellar interiors using the tools of asteroseismology, similarly to the case of other pulsating WDs such as ZZ Ceti stars or DAVs –pulsating WDs with H-rich atmospheres – and V777 Her or DBVs – pulsating WDs with He-rich atmospheres (Winget & Kepler 2008; Fontaine & Brassard 2008; Althaus et al. 2010; Córsico et al. 2019). The pulsations observed in ELMVs are compatible with global gravity (g)-mode pulsations. In the case of pulsating ELM WDs, the pulsations have large amplitudes mainly at the core regions (Steinfadt et al. 2010; Córsico et al. 2012; Córsico & Althaus 2014a), allowing for the study of their core chemical structure. According to nonadiabatic computations (Córsico et al. 2012; Van Grootel et al. 2013; Córsico & Althaus 2016), these modes are probably excited by the κ − γ (Unno et al. 1989) mechanism acting at the H-ionization zone. In the case of pre-ELMVs, the nonadiabatic stability computations for radial (Jeffery & Saio 2013) and nonradial p- and g-mode pulsations (Córsico et al. 2016; Gianninas et al. 2016; Istrate et al. 2016b) revealed that the excitation is probably due to the κ − γ mechanism, acting mainly in the zone of the second partial ionization of He, with a weaker contribution from the region of the first partial ionization of He and the partial ionization of H. The presence of He in the driving zone is crucial to having the modes destabilized by the κ − γ mechanism (Córsico & Althaus 2016; Istrate et al. 2016b).
Citation: Gianninas et al. 2016
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Citation: Gianninas et al. 2016
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An example of a low [14N/15N] value is potentially interesting for understanding the origins of material in our own solar system. The observed value in N2 of ∼200 is lower than values measured for both atmospheres of Earth and Venus (∼270; Junk & Svec 1958; Hoffman et al. 1979) and inferred for the protosolar nebula (∼440; Owen et al. 2001; Fouchet et al. 2004; Meibom et al. 2007; Marty et al. 2010). It is more similar to the extremely low values of [14N/15N] found in primitive solar system material, like cometary CN and HCN (∼140; Arpigny et al. 2003; Bockelée-Morvan et al. 2008; Manfroid et al. 2009) and in organic material in chondritic meteorites (∼50–150; Briani et al. 2009; Bonal et al. 2010), and that recently observed in HCN in a sample of T Tauri and Herbig disks (Guzmán et al. 2017). Low [14N/15N] values are seen to be correlated with high D abundances in carbonaceous chondrites, “cluster” interplanetary dust particles, and comets Wild2 and Hale-Bopp (Messenger 2000; Busemann et al. 2006; Floss et al. 2006; Aléon 2010), an enrichment that occurred either in the protosolar disk or in the precursor cloud core. Recent ISM modeling suggests that this correlation may not occur in the core stage, as a correlation between D and 15N is not expected (due to, e.g., sensitive dependence of chemistry on ortho-to-para variations in collisional partners like H2; Wirström et al. 2012; De Simone et al. 2018). This is supported by observations showing a hint of anticorrelation between the abundances of D and 15N using N2H+ in a sample of massive prestellar cores (Fontani et al. 2015b). However, the potential presence of simultaneously high 15N and D in N2 suggests that it could still be possible for this to occur in an individual core, allowing for an interstellar origin for this solar system feature. As the solar system is suggested to have formed in a rich stellar cluster experiencing a nearby supernova (Adams 2010; Dukes & Krumholz 2012; Pfalzner 2013), the environment of a massive protocluster like Sgr B2 may actually be quite relevant for understanding the neighborhood of the protosolar nebula.
Citation: Manfroid et al. 2009
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To overcome these limitations, in our previous paper (Chatzistergos et al. 2018b, Paper I, hereafter) we introduced a novel approach to process the historical and modern Ca II K observations, to perform their photometric calibration, to compensate for the intensity centre-to-limb variation (CLV, hereafter), and to account for various artefacts. By using synthetic data, we also showed that our method can perform the photometric calibration and account for image artefacts with higher accuracy than other methods presented in the literature. More importantly, we showed that, as long as the archives are consistent with each other, for example, they are centred at the same wavelength and employing the same bandwidth for the observations, the method can be used to derive accurate information on the evolution of plage areas without the need of any adjustments in the processing of the various archives (Chatzistergos et al. 2019b, Paper II, hereafter). In Paper II, we applied our method to 85 972 images from 9 Ca II K archives to derive plage areas and produce the first composite of plage areas over the entire 20th century. In particular, we analysed the Ca II K archives from the Arcetri, Kodaikanal (8-bit digitisation), McMath-Hulbert, Meudon, Mitaka, Mt Wilson, Rome/PSPT, Schauinsland, and Wendelstein sites. Five out of the nine analysed archives were amongst the most studied and prominent ones, while the remaining archives were from less studied data sources. There are, however, many other Ca II K archives that are available and still remain largely unexplored. These archives harbour the potential to fill gaps in the available plage series as well as to address inconsistencies among the various archives and within individual archives (e.g. change in data quality, or in the measuring instrument with time). Moreover, since the work presented in Paper II, more data from various historical and modern archives became available in digital form. In particular, historical data that have been made available in the meantime include those from the latest 16-bit digitisation of the Kodaikanal archive, Catania, Coimbra, Kenwood, Kharkiv, Kyoto, Manila, Rome, Sacramento Peak, and Yerkes observatories, as well as additional data from the Meudon and Mt Wilson archives. In this light, here we present results from the most comprehensive analysis to date of historical and modern Ca II K observations taken between 1892 and 2019 from 43 different datasets for the purposes of producing a composite plage area series.
Citation: Paper II
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Citation: Chatzistergos et al. 2019b
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While these similar characteristics suggest that the OA and C could have a relationship, the nature of this relationship is not clear. Kawata, Thom & Gibson (2003) used numerical simulations to investigate whether Complex C could have been produced by the passage of a satellite galaxy through the Milky Way disc, and while they found that such an event could produce a structure with the general properties of Complex C and the OA, they did not favour this hypothesis because they could not identify compelling evidence of the putative satellite. However, subsequently several stellar streams and structures have been discovered in this region of the outer Galaxy, and the progenitor(s) of these stellar structures could potentially also explain the origin of Complex C and the OA in a scenario like the one investigated by Kawata et al. (2003). The most well-known stellar stream in this region is the Monoceros Ring (e.g. Newberg et al. 2002; Peñarrubia et al. 2005), but surveys such as the Sloan Digital Sky Survey (SDSS; York et al. 2000) and the Gaia Survey (Gaia Collaboration 2016) have revealed additional stellar streams in this part of the Galaxy. Table 1 summarizes some properties of stellar streams in this direction including Monoceros ‘North’, the Anticentre Stream, Hríd, Gaia 9, and GD1. It is intriguing to note that some of the metallicities and locations of these stellar streams are similar to the published metallicities of Complex C and the OA, but as we will see in this paper, the metallicities of these HVCs are not securely measured – there are degeneracies in the ionization models used to derive metallicities, and it is possible that these HVCs have significantly higher metallicities than the published abundances. It is also worth noting that some of these stellar streams, including the northern Monoceros Ring, Hríd, and GD1, have similar velocities to the HVCs. The Anticentre Stream, on the other hand, exhibits significantly different kinematics with mean velocities of $\it {v}_{\rm LSR} = +48$ and +78 km s−1 in two directions studied by Grillmair, Carlin & Majewski (2008). However, spatially overlapping streams with different kinematics could lead to a roiled, turbulent region, which in turn could make precipitation more likely (Voit 2021). To more visually show the spatial correspondence of the stellar structures and the gas clouds, Fig. 1 shows a schematic map of the projected locations of the streams and clouds from Table 1. Note that Fig. 1 is centred and zoomed in on a set of active galactic nuclei employed in this paper (see below) and does not show the full extent of the HVCs and streams.
Citation: Peñarrubia et al. 2005
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In Fig. 9, we show the total galactic star formation rate as a function of simulation time t for each isolated disc galaxy. Following the initial vertical collapse of the disc and the subsequent star formation ‘burst’ from t ∼ 30 Myr to t ∼ 250 Myr, the SFR settles down to a rate of ∼2–4 M⊙ yr−1. We make absolutely sure to consider each isolated disc in its equilibrium state by examining the cloud population during a later time interval, between t = 600 Myr and t = 1 Gyr (grey-shaded region). Over this period, the SFR declines only gradually, by a total of around 0.5 M⊙ yr−1. These values are consistent with the current observed SFR in the Milky Way (Murray & Rahman 2010; Robitaille & Whitney 2010; Chomiuk & Povich 2011; Licquia & Newman 2015). We may also consider the resolved star-forming behaviour on scales of 750 pc, as studied in nearby galaxies by Bigiel et al. (2008). In Fig. 10, we display the star formation rate surface density as a function of gas surface density for each of our simulated galaxies, at a simulation time of 600 Myr. The top row shows the 2D projection maps of the CO-bright molecular gas column density $\Sigma _{{\rm H}_2}$. These are computed via the total gas column density in equation (35) and degraded using a Gaussian filter of FWHM = 750 pc. The corresponding projections of the star formation rate surface densities ΣSFR are displayed in the central row. Details for the production of all maps are given in Appendix A. In the bottom row, the values of $\Sigma _{{\rm H}_2}$ and ΣSFR in each pixel of the spatially degraded projection maps are compiled to produce a single histogram. The loci of our simulation data fall close to the observed star formation relations obtained by Bigiel et al. (2008), denoted by the orange contours, though with a population of points at lower densities and star formation rates than are reached by the observations. These points arise because we consider all CO-emitting gas down to a molecular hydrogen surface density of $\Sigma _{{\rm H}_2} = 10^{-3.5} \: {\rm M}_\odot {\rm pc}^{-2}$ (see Fig. 4). This avoids taking an arbitrary cut on $\Sigma _{\rm H_2}$, but also captures much lower levels of CO emission than could be detected by current observatories.
Citation: Chomiuk & Povich 2011
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Compared with BNS mergers, which would definitely eject a certain amount of materials to produce EM signals, some NSBH binaries may not tidally disrupt the NS component and, hence, would not make bright EM counterparts such as sGRBs and kilonovae.
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9
During the final merger phase for plunging NSBH binaries, some weak EM signals may be produced because of the charge and magnetic field carried by the NS (e.g., Dai 2019; Pan & Yang 2019; Zhang 2019; D’Orazio et al. 2022; Sridhar et al. 2021). The tidal disruption probability of NSBH mergers and the brightness of NSBH EM signals are determined by the BH mass, BH spin, NS mass, and NS equation of state (EoS; e.g., Belczynski et al. 2008; Kyutoku et al. 2011, 2013, 2015; Fernández et al. 2015; Kawaguchi et al. 2015, 2016; Foucart 2012; Foucart et al. 2018; Barbieri et al. 2019; Krüger & Foucart 2020; Fragione & Loeb 2021; Fragione 2021; Zhu et al. 2020, 2021c, 2021e; Raaijmakers et al. 2021; Li & Shen 2021; Tiwari et al. 2021). An NSBH merger tends to be a disrupted event and produces bright EM signals if it has a low-mass BH with a high projected aligned spin and a low-mass NS with a stiff EoS. The parameter space in which an NSBH merger can undergo tidal disruption may be very limited. Recently, LIGO–Virgo–KAGRA (LVK) Collaboration reported three high-confidence GWs from NSBH candidates, i.e., GW190814, GW200105_162426, and GW200115_042309 (Abbott et al. 2020, 2021a; Nitz et al. 2021). In spite of many efforts for follow-up observations of these three events, no confirmed EM counterpart candidate has been identified (e.g., Coughlin et al. 2020; Gompertz et al. 2020; Kasliwal et al. 2020;Page et al. 2020; Thakur et al. 2020; Alexander et al. 2021; Anand et al. 2021; Dobie et al. 2022; Kilpatrick et al. 2021). Abbott et al. (2021a), Zhu et al. (2021c), and Fragione (2021) showed that the parameter space of these GW candidates mostly lies outside the disrupted parameter region, so these candidates are likely plunging events with a high probability. There are many mysteries surrounding NSBH binaries, such as the proportion of disrupted events in cosmological NSBH mergers, their cosmological contribution to elements heavier than iron, the formation channel of NSBH binaries, and so on. Systemic research on the population properties of NSBH binaries can help us address these mysteries and unveil the nature of cosmological NSBH binaries.
Citation: Krüger & Foucart 2020
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To investigate the emission-line properties in the blue system, we employed the photoionization code Cloudy (Version 17.01, Ferland et al. 2017) and applied the measured emission-line ratios to these models to simulate the possible physical conditions and processes in the medium. The simple model is a slab-shaped gas with a unique density and homogeneous chemical composition of solar values, irradiated directly by the central ionization continuum source. For the BLR around one of the hypothesized binary black holes, such primordial models can be simply described using parameters such as density nH, hydrogen column density NH, ionization parameter U, and spectral energy distribution (SED) of the incident radiation. A typical AGN ionization continuum is applied as the incident SED, which is a combination of a blackbody “Big Bump” and power laws.6

6
See details in Hazy, a brief introduction to Cloudy; http://www.nublado.org.
 The component peaks at ≈1 Ryd and is parameterized by TBB = 1.5 × 105 K. The slope of the X-ray component, the X-ray to UV ratio, and the low-energy slope are set as αx = −2 (beyond 100 keV) and −1 (between 1.36 eV and 100 keV), αox = −1.4, and αUV = −0.5, respectively. This UV-soft SED is regarded as more realistic for radio-quiet quasars than the other available SEDs provided by Cloudy (see the detailed discussion in Section 4.2 of Dunn et al. 2010). We calculated a series of photoionization models with different ionization parameters, densities, and hydrogen column densities. The ranges of these parameters are −4.0 ≤ log10 U ≤ 1.0, 3.0 ≤ log10 nH (cm−3) ≤ 11.0, and 19.0 ≤ log10 NH (cm−2) ≤ 24.0, with a step of 0.2 dex, which could well cover the possible parameter space of the broad-line and narrow-line regions. In Figure 3, the flux ratios of He iλ10830/Hα are presented in the log U–log NH space for the five densities (log nH (cm−3) = 3, 5, 7, 9, and 11). The extensive parameter space is almost enough to cover all the routine possibilities of the AGN “normal” emission-line regions. However, the typical BLR gases with nH ∼ 109–1010 cm−3, NH ∼ 1022 cm−2 and U ∼ 10−2–10−1 present the relatively strong He i λ10830 emission. If the blue system of SDSS J1536+0441 is also compared, the observed ratio of He i10830/Hα6564 is at least larger than 0.1, which is two times the 3σ upper limit. Further extensive calculation in a larger parameter space suggests that a parameter combination range of UnH ≈ 1011.5 cm−3 with an exceedingly high density of nH ≥ 1012 cm−3 would reproduce the observed flux ratios of the hydrogen and helium lines. If the blue system emits from such a high-density medium, the size would be 50 times less than that of the red system BLR (based on the sub-parsec binary hypothesis, in which both BLRs are illuminated by the same ionizing flux), and the number ratios of ions in the blue system and red system would be only approximately five per thousand. Even accounting for the higher emission efficiency (within an order of magnitude), the high-density medium is not sufficient to emit blue system lines comparable to those of the red system.
Citation: Dunn et al. 2010
Citation function: Uses
In addition to the wind models of λ And, we also present here the first full surface magnetic field observations of this star, finding a strong magnetic field for such an evolved star. These observations, carried out with the NARVAL spectropolarimeter, allow us to constrain the surface magnetic field of λ And. These derived surface magnetic fields can constrain the lower boundary of the 3D magnetohydrodynamic wind simulations that we run. Usually, we see a decay in magnetic field strength as solar-type stars evolve, as their activity decreases along with their rotation (Skumanich 1972; Vidotto et al. 2014b; Booth et al. 2020). However, this subgiant star seems to have a relatively strong large-scale magnetic field compared to the Sun. The exact process through which this star would reach this stage in its evolution with such a magnetic field is yet unknown. Potential reasons are that it began with a much stronger dynamo in its past than anticipated, or perhaps the secondary companion had some effect on the primary star at a point in the past. λ And differs from the Sun as it is an RS Canum Venaticorum (RS CVn) variable, meaning it is a variable binary system. The variability on this star is likely due to magnetic spots coming in and out of view due to stellar rotation (Baliunas & Dupree 1979, 1982; Donati, Henry & Hall 1995; Henry et al. 1995; O’Neal et al. 2001; Sanz-Forcada, Brickhouse & Dupree 2001; Frasca et al. 2008; Drake et al. 2011). RS CVn systems, in particular, can present observed levels of chromospheric and coronal activity that are orders of magnitude higher than in single stars with similar spectral types (Ayres & Linsky 1980; Walter & Bowyer 1981). This is likely caused by the increase in activity when the two stars interact with each other, which can lead to rotational synchronization of the system (e.g. Lanza & Rodonò 2004; an analogous process has been inferred to take place in close-in planet–star systems, Cuntz, Saar & Musielak 2000). For the purposes of this work, we assume the binarity of this system does not affect our wind models. Compared to the Sun, λ And is metal-poor ([Fe/H] = −0.46 ± 0.04 dex, Maldonado & Villaver 2016). We do not include the effects of different metal abundances on the stellar wind and stellar evolution, but the effects of which have been examined in other works (Suzuki 2018).
Citation: Vidotto et al. 2014b
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We also examine our 





 measurement of NGC 3504 in the context of the empirical compilations of 





 and 





 scaling relations (Kormendy & Ho 2013; McConnell et al. 2013; Scott et al. 2013; Saglia et al. 2016) in Figure 16. The stellar-bulge velocity dispersion of NGC 3504 is determined from Ho et al. (2009), while the bulge mass of 





M⊙ was derived from Section 2.2. For a sanity check, we estimate the bulge mass of NGC 3504 using our H-band MGE model and adapting the effective radius of the bulge derived from the bulge-disk-bar decomposition model (Laurikainen et al. 2004). Accounting for the dynamical M/LH (Section 5.2), we obtain 





M⊙. Our result shows that the best-fit 





 of NGC 3504 is fully consistent with the empirical 





 and 





 relations of Kormendy & Ho (2013), McConnell et al. (2013), and Saglia et al. (2016), but outside 





 uncertainty of the Scott et al. (2013) and Savorgnan et al. (2016) empirical 





 relations for “Sérsic” galaxies (those without central cores). Compared with the theoretical predictions of the bimodality in the BH accretion efficiency model (e.g., Pacucci et al. 2015, 2018), our measurement is consistent with the 





 correlation, but a positive outlier is the 





 relation up to 1σ. At the mass of 





 M⊙, the SMBH of NGC 3504 lies within the same mass regime as the BHs derived in the Combes et al. (2019) sample and lies between the samples of lower- and higher-mass galaxies previously and currently studied with ALMA (Davis et al. 2013, 2017, 2018; Onishi et al. 2015, 2017; Barth et al. 2016a, 2016b; Boizelle et al. 2019; Nagai et al. 2019; North et al. 2019; Smith et al. 2019, T. Davis et al. 2020, in preparation, D. Nguyen et al. 2020, in preparation), respectively. All of these works prove that the cold gas-dynamical method observed with ALMA at high spatial resolution now can work well in a wide range of BH masses covering six orders of magnitude from 105 to 





.
Citation: Laurikainen et al. 2004
Citation function: Uses