adsabs/AstroCLIMB huggingface dataset:
Paper: Discovery of a Premerger Shock in an Intercluster Filament in Abell 98
Authors: Arnab Sarkar, Scott Randall, Yuanyuan Su, Gabriella E. Alvarez, Craig Sarazin, Paul Nulsen, Elizabeth Blanton, William Forman, Christine Jones, Esra Bulbul, John Zuhone, Felipe Andrade-Santos, Ryan E. Johnson, Priyanka Chakraborty
Figure caption: Comparison of the temperature profile across the shock front with the predicted electron temperature profiles based on the instant collisionless model (red) and the Coulomb collisional model (blue). Yellow ellipse indicates the relevant postshock electron temperature for comparing with two models.
Paper: Limits on Hierarchical Black Hole Mergers from the Most Negative χ eff Systems
Authors: Maya Fishbach, Chase Kimball, Vicky Kalogera
Figure caption: Inferred χ eff CDF for the astrophysical BBH population (left) and posterior PDF on the fraction of χ eff < −0.3 (right). We infer the χ eff distribution by fitting the confident BBH events in GWTC-3 to two models, a Gaussian (blue) and a mixture model between a Gaussian and a uniform distribution (orange), both truncated to the physically allowed range −1 < χ eff < 1. Solid lines show the median CDF value at each χ eff, and shaded regions show 90% credible intervals. Both models assume that the χ eff distribution does not vary with BBH mass. The mixture model is designed to allow for more support at the tails of the χ eff distribution and so allows for a higher fraction of systems with χ eff < −0.3. The constraints on the χ eff < −0.3 fraction can be interpreted as limits on the contribution of HMs to the astrophysical BBH population (right panel, top axis).
Paper: Limits on Hierarchical Black Hole Mergers from the Most Negative χ eff Systems
Authors: Maya Fishbach, Chase Kimball, Vicky Kalogera
Figure caption: Theoretical distribution of χ eff among BBHs in which one (orange) or both (blue) components are the products of previous mergers. Top panel: χ eff PDF for four different assumptions about the initial spins χ 1g and mass ratios q 1g of 1g+1g BHs: χ 1g = 0 and a uniform q 1g distribution 0.8 < q 1g < 1 (default; thick blue and filled orange), χ 1g = 0 and 0.5 < q 1g < 1 (thin solid lines), uniform 0 < χ 1g < 0.5 and 0.8 < q 1g < 1 (thin dashed lines), and 0 < χ 1g < 0.5 and 0.5 < q 1g < 1 (thin dotted lines). The mass ratios of mixed-generation 1g+2g mergers are always assumed to be given by 1/(1 + q 1g), where q 1g is drawn from the assumed mass ratio distribution for 1g+1g mergers. Bottom panel: corresponding CDFs, shown just for the default spin and mass ratio assumptions.
Paper: Limits on Hierarchical Black Hole Mergers from the Most Negative χ eff Systems
Authors: Maya Fishbach, Chase Kimball, Vicky Kalogera
Figure caption: Fraction of systems with χ eff < 0 (top panel) and χ eff < −0.3 (bottom panel) at each primary mass m 1, inferred by fitting a mass-dependent χ eff distribution. The bottom axis shows primary mass in solar masses, while the top axis shows the corresponding quantile in the marginal m 1 posterior population distribution. In each panel, the orange dashed line shows the median value at each m 1 inferred under the m 1-varying Gaussian + Uniform Mixture model, while the green solid line shows the median for the m 1-varying Gaussian model. The inner orange dotted lines (dark green shaded region) enclose the symmetric 50% credible interval for the mixture (Gaussian) model. In the top panel, the outer orange dotted lines (light green shaded region) enclose the symmetric 90% credible interval for the two models, while in the bottom panel, we show the 90% upper limit, because the posterior peaks at HM fraction = 0 for all m 1. Marginalizing over the mass distribution, the total HM fraction across all masses is less than 1.3% (Gaussian model) or 26% (mixture model; 90% credibility).
Paper: Limits on Hierarchical Black Hole Mergers from the Most Negative χ eff Systems
Authors: Maya Fishbach, Chase Kimball, Vicky Kalogera
Figure caption: Expected number of BBH events with χ eff as the total number of observations increases. We plot 2000 realizations, where each realization is drawn from the hyperposterior of the m 1-varying Gaussian + Uniform Mixture model. Each realization is colored by the corresponding HM fraction. Larger HM fractions predict more events with χ eff < −0.3, especially as the total number of events approaches 500.
Paper: Magnetar Engines in Fast Blue Optical Transients and Their Connections with SLSNe, SNe Ic-BL, and lGRBs
Authors: Jian-Feng Liu, Jin-Ping Zhu, Liang-Duan Liu, Yun-Wei Yu, Bing Zhang
Figure caption: Relationship between ejecta masses of FBOTs and initial spin periods of FBOT magnetars (red points). The green, blue, and violet points correspond to the cases of SLSNe (Yu et al. 2017), GRB-SNe (Lü et al. 2018), and SNe Ic-BL (Lyman et al. 2016; Taddia et al. 2019), respectively. The best-fitting log-linear relation ﹩{P}_{{\rm{i}}}\propto {M}_{\mathrm{ej}}^{-0.41}﹩ is shown by the dashed line. The top and right panels display the number distributions of ejecta masses and initial NS periods, derived by the method of kernel density estimation, for these four types of explosions.
Paper: Magnetar Engines in Fast Blue Optical Transients and Their Connections with SLSNe, SNe Ic-BL, and lGRBs
Authors: Jian-Feng Liu, Jin-Ping Zhu, Liang-Duan Liu, Yun-Wei Yu, Bing Zhang
Figure caption: Magnetic field strengths of FBOT magnetars against the initial spin periods (red points). Magnetar parameters for SLSNe (green points) and lGRBs (blue points) are collected from Yu et al. (2017) and Lü & Zhang (2014), respectively. Orange and blue dashed lines represent the parallel fitting Pi–B p anticorrelations of the magnetars for the FBOTs plus the SLSNe and lGRBs, respectively. The probability density functions of the magnetic field strength and initial spin period distributions for these three types of explosions are displayed in the top and right panels, respectively.
Paper: Magnetar Engines in Fast Blue Optical Transients and Their Connections with SLSNe, SNe Ic-BL, and lGRBs
Authors: Jian-Feng Liu, Jin-Ping Zhu, Liang-Duan Liu, Yun-Wei Yu, Bing Zhang
Figure caption: Left panel: Peak absolute magnitudes against the rise times for FBOTs (red points), SLSNe (green points), GRB-SNe (blue points), and SNe Ic-BL (purple points). The solid, dashed, and dotted lines are the conditions of M Ni = 0.3M ej, 0.1M ej, and 0.03M ej, respectively. Right panel: Decline times against the rise times for these four types of explosions. The dashed–dotted line, i.e., t decl ≈ 1.8t rise, corresponds to t sd = t diff. The dotted lines represent the different relationships between these two timescales as labeled.
Paper: A New Cold Stream near the Southern Galactic Pole
Authors: Yong Yang, Jing-Kun Zhao, Xiang-Xiang Xue, Xian-Hao Ye, Gang Zhao
Figure caption: The left panel is a 2D histogram of stars in CMD with PMs selected and background subtracted. The blue dashed line represents the best-fit isochrone with Age = 12 Gyr and [M/H] = −2.0 dex at DM = 14.9 mag. The right panel is a 2D histogram of PMs after CMD selection and background subtraction. The filters of Figure 1 within 29° < ϕ 1 < 87° are overplotted in the blue line. Both of the diagrams are smoothed with a 2D Gaussian kernel of σ = 1 pixel. The red polygons represent the CMD and PM selections applied to the stream and off-stream regions.
Paper: A New Cold Stream near the Southern Galactic Pole
Authors: Yong Yang, Jing-Kun Zhao, Xiang-Xiang Xue, Xian-Hao Ye, Gang Zhao
Figure caption: The upper and lower panels present the dust extinction map extracted from Schlegel et al. (1998) and Gaia's scanning pattern covered by the EDR3, respectively. The middle panel presents the weighted sky map. The blue arrow points to the SMC. Stars within the green rectangle are used to create the lateral profile of SGP-S. The red dashed line of the three panels indicates the trajectory of the stream.
Paper: A New Cold Stream near the Southern Galactic Pole
Authors: Yong Yang, Jing-Kun Zhao, Xiang-Xiang Xue, Xian-Hao Ye, Gang Zhao
Figure caption: The lateral distributions along ϕ 2 for weighted (red solid) and unweighted (blue dashed) numbers of stars within the green rectangle of Figure 2.
Paper: A New Cold Stream near the Southern Galactic Pole
Authors: Yong Yang, Jing-Kun Zhao, Xiang-Xiang Xue, Xian-Hao Ye, Gang Zhao
Figure caption: The left panel displays GCs (black points) and SGP-S (red circle) in angular momenta and energy space. The right panel presents projections of streams and orbits in ICRS frame. The red track and black line indicate SGP-S and its best-fit orbit. Colored lines represent orbital paths for GC NGC 5824 integrated in different potential models. Numbered tracks represent 12 known streams obtained from Mateu (2022). The black cross denotes the southern Galactic pole.
Paper: Magnetar Engines in Fast Blue Optical Transients and Their Connections with SLSNe, SNe Ic-BL, and lGRBs
Authors: Jian-Feng Liu, Jin-Ping Zhu, Liang-Duan Liu, Yun-Wei Yu, Bing Zhang
Figure caption: Multiband observations and fittings for the FBOTs by the magnetar-powered model.
Paper: A New Cold Stream near the Southern Galactic Pole
Authors: Yong Yang, Jing-Kun Zhao, Xiang-Xiang Xue, Xian-Hao Ye, Gang Zhao
Figure caption: The PM filters used to weight stars with Equation (2). ϕ 1 is the longitude in a rotated frame with a pole of (α = 270°, δ = 0°). The red line denotes the ﹩{\mu }_{\alpha }^{* }﹩ medians of NGC 5824 model stream particles in each ϕ 1 bin with a bin width of 1.°1 mas yr−1 is further added to their μ  δ  medians; it is shown with the blue line.
Paper: Magnetar Engines in Fast Blue Optical Transients and Their Connections with SLSNe, SNe Ic-BL, and lGRBs
Authors: Jian-Feng Liu, Jin-Ping Zhu, Liang-Duan Liu, Yun-Wei Yu, Bing Zhang
Figure caption: Posteriors for magnetar model fit to DES 16C3gin. Medians and 1σ ranges are labeled.
Paper: HD 56414 b: A Warm Neptune Transiting an A-type Star
Authors: Steven Giacalone, Courtney D. Dressing, A. García Muñoz, Matthew J. Hooton, Keivan G. Stassun, Samuel N. Quinn, George Zhou, Carl Ziegler, Roland Vanderspek, David W. Latham, S. Seager, Joshua N. Winn, Jon M. Jenkins, César Briceño, Chelsea X. Huang, David R. Rodriguez, Avi Shporer, Andrew W. Mann, David Watanabe, Bill Wohler
Figure caption: Top: TESS light curve produced by the SPOC pipeline after flattening and outlier removal. Blue triangles show the times of transits used for fitting. The sectors are indicated at the top of the panel. Sector 4 was removed from the light-curve analysis (see Section 2.1). Bottom left: SED fit of HD 56414. Blue points indicate broadband photometry measurements, and the black curve indicates the best-fit stellar model with T eff = 8500 ± 150 K. Bottom right: phase-folded TESS data centered on the transit with residual variability removed with a Gaussian process model. The data are binned with bin widths of 30 s (gray points) and 30 minutes (black points). The blue line is the best-fit transit model.
Paper: HD 56414 b: A Warm Neptune Transiting an A-type Star
Authors: Steven Giacalone, Courtney D. Dressing, A. García Muñoz, Matthew J. Hooton, Keivan G. Stassun, Samuel N. Quinn, George Zhou, Carl Ziegler, Roland Vanderspek, David W. Latham, S. Seager, Joshua N. Winn, Jon M. Jenkins, César Briceño, Chelsea X. Huang, David R. Rodriguez, Avi Shporer, Andrew W. Mann, David Watanabe, Bill Wohler
Figure caption: Visualizations of the vetting measures described in Section 4. Top left: objects within 100″ of HD 56414 (indicated by the yellow star). The SPOC aperture is shown in red, squares are nearby sources bright enough to be FP-inducing nearby eclisping binaries, and circles are nearby sources too faint to be FP-inducing nearby eclipsing binaries. Top right: corresponding TESS image, with the same aperture overlaid. Bottom left: Speckle imaging image and contrast curve of HD 56414, which detects no companions within detection limits. Bottom right: results of centroid offset analysis with vetting. HD 56414 is at the origin. Solid black lines are the 1σ, 2σ, and 3σ contours formed from 3629 randomly sampled out-of-transit data points. Blue points are centroids for each in-transit data point. The difference between the two resulting distributions is not statistically significant.
Paper: HD 56414 b: A Warm Neptune Transiting an A-type Star
Authors: Steven Giacalone, Courtney D. Dressing, A. García Muñoz, Matthew J. Hooton, Keivan G. Stassun, Samuel N. Quinn, George Zhou, Carl Ziegler, Roland Vanderspek, David W. Latham, S. Seager, Joshua N. Winn, Jon M. Jenkins, César Briceño, Chelsea X. Huang, David R. Rodriguez, Avi Shporer, Andrew W. Mann, David Watanabe, Bill Wohler
Figure caption: Simulated atmospheric mass-loss rates as a function of orbital separation for planets with the same size as HD 56414 b orbiting a star identical to HD 56414. Each line represents a planet of a different mass. Assuming a core-to-envelope mass fraction of ∼10%, planets at 0.229 au with M p = 8 M ⊕ can lose over a third of their atmospheric mass over the typical 1 Gyr lifetime of an A-type star. Closer-in planets with M p < 14 M ⊕ are susceptible to losing all of their atmospheres over this timescale.
Paper: First Constraining Upper Limits on Gravitational-wave Emission from NS 1987A in SNR 1987A
Authors: Benjamin J. Owen, Lee Lindblom, Luciano Soares Pinheiro
Figure caption: The left panel displays points representing direct observational 90% confidence upper limits on the intrinsic strain h 0 from NS 1987A as a function of frequency in 1 Hz bands for our search. The (red) horizontal line in the left panel indicates the indirect limit ﹩{h}_{0}^{\mathrm{age}}﹩ from energy conservation. The right panel shows derived upper limits on the fiducial dimensionless neutron star ellipticity, ϵ, and r-mode amplitude, α, based on these h 0 upper limits. The h 0 data shown in the left panel is available in machine-readable format as the data behind the figure.(The data used to create this figure are available.)
Paper: HD 56414 b: A Warm Neptune Transiting an A-type Star
Authors: Steven Giacalone, Courtney D. Dressing, A. García Muñoz, Matthew J. Hooton, Keivan G. Stassun, Samuel N. Quinn, George Zhou, Carl Ziegler, Roland Vanderspek, David W. Latham, S. Seager, Joshua N. Winn, Jon M. Jenkins, César Briceño, Chelsea X. Huang, David R. Rodriguez, Avi Shporer, Andrew W. Mann, David Watanabe, Bill Wohler
Figure caption: Confirmed transiting planets (cyan squares for A-type host stars; black dots for other host stars) and HD 56414 b (yellow star) in different parameter spaces. Error bars for planets orbiting A-type stars are shown but are often smaller than the scale of the image. The three sub-Jovian cyan squares are (in order of increasing orbital period) Kepler-1115 b, Kepler-462 b, and Kepler-462 c. HD 56414 b is the second shortest-period sub-Jovian planet known to exist around an A-type star and has one of the hottest host stars of any known sub-Jovian planet. Data acquired from the NASA Exoplanet Archive.
Paper: Typhon: A Polar Stream from the Outer Halo Raining through the Solar Neighborhood
Authors: Wassim Tenachi, Pierre-Antoine Oria, Rodrigo Ibata, Benoit Famaey, Zhen Yuan, Anke Arentsen, Nicolas Martin, Akshara Viswanathan
Figure caption: Actions and total energy of Typhon members (indicated by star symbols) and of the 573 preselected stars having ϖ/δ ϖ > 10, r apo > 75 kpc, and d ⊙ < 4 kpc (denoted by circles). Stars are colored by their apocenter values in the top panel and and by their vertical action values in the bottom row of panels. Top panel: (J  ϕ , J  z ) plane used for the selection where the overdensity was discovered. The most significant detection obtained using a Hough transform technique (Illingworth & Kittler 1988) on stars with J  z  > 1000 kpc km s−1 (i.e., with large departures from the Galactic midplane) is shown with a red line. This line runs through the Typhon structure. The parallelogram selection of the structure is depicted in a solid line encompassing 16 stars, and is defined by J  z  ∈ [2000, 3100] kpc km s−1 and 3.3J  ϕ  + 3500 kpc km s−1 < J  z  < 3.3J  ϕ  + 5000 kpc km s−1. The symmetric (retrograde) selection with respect to the J  ϕ  = 0 line is shown with a dashed line. Bottom left and bottom right panels show the (J  ϕ , J  r ) and (J  ϕ , E tot) planes, respectively.
Paper: Typhon: A Polar Stream from the Outer Halo Raining through the Solar Neighborhood
Authors: Wassim Tenachi, Pierre-Antoine Oria, Rodrigo Ibata, Benoit Famaey, Zhen Yuan, Anke Arentsen, Nicolas Martin, Akshara Viswanathan
Figure caption: Positions and velocity vectors in galactic Cartesian coordinates of Typhon sample members. Velocity vectors scale 1: 3 × 103. The sample shows very clear streaming motion. For reference, the position and velocity vector of the Sun is also shown in red.
Paper: A Robust Test of the Existence of Primordial Black Holes in Galactic Dark Matter Halos
Authors: Marek Abramowicz, Michał Bejger, Andrzej Udalski, Maciek Wielgus
Figure caption: Ratio of the density of LBHs to NSs in a model galaxy of 13 Gyr age, as a function of M PBH, the characteristic mass of PBHs, for 3 different fractions of PBHs in a galactic-mass composition ξ. This ratio represents the expected ratio of the occurrence of collisions of stellar-mass BHs with LBHs and stellar-mass BHs with NSs. The three panels correspond to the galactic disk, bulge, and the total galaxy. For a large ξ or light M PBH, the majority of NSs may become LBHs.
Paper: Discovery of γ-Ray Pulsations from PSR J1835–3259B in the Globular Cluster NGC 6652
Authors: Pengfei Zhang, Yi Xing, Zhongxiang Wang
Figure caption: Timing analysis results for PSR J1835−3259B. (A) The integrated weighted γ-ray pulse profile (16 phase bins). (B) Two-dimensional phaseogram (16 phase bins), where the bottom color bar indicates the weights of the photons (with the largest being 88%). (C) H-test values over the span of the data. (D) Schematic radio pulse profile of PSR J1835−3259B drawn from that reported in Gautam et al. (2022) for comparison. Red arrows indicate the mini-peak seen in both γ-rays and radio.
Paper: Hubble Space Telescope Imaging Reveals That SN 2015bh Is Much Fainter than Its Progenitor
Authors: Jacob E. Jencson, David J. Sand, Jennifer E. Andrews, Nathan Smith, Jay Strader, Mojgan Aghakhanloo, Jeniveve Pearson, Stefano Valenti
Figure caption: Left: CMD from the F555W and F814W imaging of SN 2015bh, including a detection of the progenitor in 2008 (light-red circle; Elias-Rosa et al. 2016) and new late-time points from 2017 to 2019 (red circles). Late-time points for SN 2009ip (blue squares; Smith et al. 2016a, 2022) and AT 2016jbu (dark-green diamond; Brennan et al. 2022c) are also shown. For the AT 2016jbu progenitor (light-green diamond), the arrow represents the A  V  = 1 mag reddening vector (Kilpatrick et al. 2018). All phases are relative to the transient peak. Right: HRD depicting the late-time evolution of SN 2015bh (red circles) and SN 2009ip (blue squares). Unfilled points are based on ground-based data and reproduced from Thöne et al. (2017; see their Figure 15), while new points for SN 2015bh are shown as filled symbols. The evolution shown assumes a constant temperature between the last two epochs, but an evolution to higher temperatures ≲20,000 K with a smaller drop in luminosity at t = 975 days is also consistent with observations. The inferred properties of the progenitor stars are indicated by the shaded regions, including from the 1999 HST photometry of SN 2009ip (cyan; Smith et al. 2010; Foley et al. 2011), the 2016 HST photometry of AT 2016jbu (light green; Kilpatrick et al. 2018; Brennan et al. 2022c), the 2008–2009 HST photometry of SN 2015bh (light red; Elias-Rosa et al. 2016), and from modeling of the SN 2015bh 2013 progenitor spectrum (light red; Boian & Groh 2018). Nonrotating, solar-metallicity stellar evolution tracks from MIST (Choi et al. 2016) are shown for comparison as black curves for a range of initial masses in both panels.
Paper: Hubble Space Telescope Imaging Reveals That SN 2015bh Is Much Fainter than Its Progenitor
Authors: Jacob E. Jencson, David J. Sand, Jennifer E. Andrews, Nathan Smith, Jay Strader, Mojgan Aghakhanloo, Jeniveve Pearson, Stefano Valenti
Figure caption: The long-term pre- and postexplosion light curves of SN 2015bh, corrected for foreground extinction with E(B − V) = 0.23 mag. HST photometry, including archival data from Elias-Rosa et al. (2016) and newly presented late-time imaging, are shown as filled symbols. The late-time photometry has faded far below the observed levels of the progenitor at F555W (dotted–dashed cyan line) and F814W (dashed red line) in the 2008–2009 pre-explosion data. The 1999 progenitor level of SN 2009ip at F 606 W (dotted black line) is also shown for reference, corrected for extinction with A  R  = 0.05 mag as in Smith et al. (2010). Ground-based VRI-band light curves of SN 2015bh from Goranskij et al. (2016), Ofek et al. (2016), and Elias-Rosa et al. (2016) are shown as open symbols. Spectroscopic observation epochs during the 2013 precursor eruptions (Ofek et al. 2016, see also Figure 4) and our new late-time observations are indicated by vertical black bars and “S” symbols.
Paper: Hubble Space Telescope Imaging Reveals That SN 2015bh Is Much Fainter than Its Progenitor
Authors: Jacob E. Jencson, David J. Sand, Jennifer E. Andrews, Nathan Smith, Jay Strader, Mojgan Aghakhanloo, Jeniveve Pearson, Stefano Valenti
Figure caption: SEDs from HST photometry of SN 2015bh in 2017 (yellow circles), 2018 (orange, thin diamonds), and 2019 (red, thick diamond). The best-fit blackbody spectrum (T BB = 8530 K, R BB = 280 R ⊙) to the 2017 data (excluding F 625 W) is shown as the yellow dashed curve and the yellow shaded regions represents the 16th–84th percentile uncertainties from the MCMC. The 2008–2009 HST photometry of the progenitor from Elias-Rosa et al. (2016) is shown as black squares, where the lines connect contemporaneous points. The black dotted curves show ATLAS synthetic stellar spectra (Castelli & Kurucz 2003) with the properties inferred for the progenitor listed in Table 4 of Elias-Rosa et al. (2016). The observed 2013 spectrum of the progenitor from Ofek et al. (2016) is shown in gray. Finally, the dotted purple, indigo, and blue curves represent model Starburst99 clusters at ages of 5, 10 and 20 Myr, respectively, as described in the main text.
Paper: Hubble Space Telescope Imaging Reveals That SN 2015bh Is Much Fainter than Its Progenitor
Authors: Jacob E. Jencson, David J. Sand, Jennifer E. Andrews, Nathan Smith, Jay Strader, Mojgan Aghakhanloo, Jeniveve Pearson, Stefano Valenti
Figure caption: Late-time MMT Blue Channel spectrum of the site of SN2015bh in the rest frame of NGC 2770 (z = 0.00649, from NED). The extraction aperture is shown overlaid on the reduced 2D spectrum at the top of the figure. Rest-frame wavelengths of emission features typical of H II regions are indicated by the vertical lines and labeled by atomic species. The spectrum has been dereddened only for Milky Way extinction to NGC 2770. The observed lines are at a velocity of −40 km s−1 compared to the systemic velocity of NGC 2770, consistent with the galaxy’s rotation curve (Márquez et al. 2002).
Paper: Typhon: A Polar Stream from the Outer Halo Raining through the Solar Neighborhood
Authors: Wassim Tenachi, Pierre-Antoine Oria, Rodrigo Ibata, Benoit Famaey, Zhen Yuan, Anke Arentsen, Nicolas Martin, Akshara Viswanathan
Figure caption: Left: likelihood contours of the mean metallicity and metallicity dispersion of the spectroscopic sample, shown for the full seven-star sample (black lines), and removing the most metal-poor star (gray lines). Right: color–magnitude diagram of the sample members of Typhon. For reference, the gray line shows a PARSEC isochrone model (Bressan et al. 2012) of age 12.5  Gyr and of metallicity [Fe/H] = −1.60 dex. The reasonable correspondence of this model shows that the population is predominantly very old.