J/MNRAS/522/847 Stellar properties of M3/M13 HB stars with UVIT (Kumar+, 2023) ================================================================================ Globular Cluster UVIT Legacy Survey (GlobULeS) - II. Evolutionary status of hot stars in M3 and M13. Kumar R., Pradhan A.C., Sahu S., Subramaniam A., Piridi S., Cassisi S., Ojha D.K. =2023MNRAS.522..847K (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Clusters, globular ; Stars, horizontal branch ; Ultraviolet ; Photometry ; Positional data ; Effective temperatures ; Magnitudes, absolute ; Stars, diameters ; Stars, distances Keywords: Hertzsprung-Russell and colour-magnitude diagrams - stars: horizontal branch - white dwarfs - globular clusters: individual: NGC 5272 (M3) and NGC 6205 (M13) - ultraviolet: stars Abstract: We present a far-ultraviolet (FUV) study of hot stellar populations in the second parameter pair globular clusters (GCs) M3 and M13, as a part of the GC UVIT Legacy Survey programme (GlobULeS). We use observations made with F148W and F169M filters of the Ultraviolet Imaging Telescope (UVIT) onboard AstroSat along with ground-based data (UBVRI filters), Hubble Space Telescope(HST) GC catalogue, and Gaia EDR3 catalogue. Based on the FUV-optical colour-magnitude diagrams, we classify the sources into the horizontal branch (HB) stars, post-HB stars, and hot white dwarfs (WDs) in both the GCs. The comparison of synthetic and observed colours of the observed HB stars suggests that the mass-loss at the red giant branch and He spread in both clusters have a simultaneous effect on the different HB distributions detected in M3 and M13, such that HB stars of M13 require a larger spread in He (0.247-0.310) than those of M3 (Y = 0.252-0.266). The evolutionary status of HB stars, post-HB stars, and WDs are studied using SED fit parameters and theoretical evolutionary tracks on the H-R diagram. We found that the observed post-HB stars have evolved from zero-age HB (ZAHB) stars of the mass range of 0.48-0.55 M_{sun}_ in M3 and M13. We detect 24 WD candidates in each cluster having log(Lbol/L_{sun}_) in the range of -0.8 to +0.6 and log(Teff/K) in the range of 4.2-5.0. Placing the WDs on the H-R diagram and comparing them with models, it is found that M13 has a population of low-mass WDs, probably originating from binary evolution. Description: M3 (NGC 5272) and M13 (NGC 6205) are regarded as two twin globular clusters (GCs) in many aspects. They have been studied extensively photometrically, particularly, in optical and ultraviolet (UV) wavebands to explore the peculiar features of their horizontal branch (HB) stars. Despite having similar metallicity ([Fe/H] ~-1.5 dex) and age (~12.5 Gyr) their HB morphologies are different. The Ultraviolet Imaging Telescope (UVIT) onboard AstroSat has been playing an important role in exploring the hot HB stars in UV in several GCs. In this paper, we aim to perform a comprehensive study of the HB morphology of M3 and M13 GCs and explore their further evolutionary status, such as AGB-manque, PEAGB, post-AGB and hence, the final product, WDs, in both the clusters. As exposed in section 2, we observed M3 and M13 in two FUV filters, F148W and F169M of UVIT. The observation, photometry, and cluster membership details of the observed sources are provided in Sahu et al. (2022MNRAS.514.1122S). The total number of sources detected in M3 and M13 are 878 and 1090, respectively.We retain only those sources that have a cluster membership probability of more than 90 per cent in the catalogue. Finally, we were left with 274 (399) stars in the inner region (HST counterparts) and 160 (390) stars in the outer region (Gaia counterparts) of the cluster M3 (M13). The Gaia counterparts were then cross-matched with the ground-based photometric catalogue to obtain the magnitudes in U, B, V, R, and I filters (Stetson et al. 2019MNRAS.485.3042S, Cat. J/MNRAS/485/3042). All the observed sources were extinction corrected using the extinction values (E(B-V) = 0.011 mag for M3 and 0.014 mag for M13). Next, thanks to CMD diagrams as explained in section 3, we divide the observed HB stars on the basis of temperature into three subpopulations as bHb blue HB (7750 K <= Teff <= 11500 K), intermadiate iHb HB (11500 K <= Teff <= 20000 K), extreme eHb HB (20000 K <= Teff <= 30000K). We have used BaSTI-IAC ZAHB isochrones locus to co-relate the Teff of HB stars with different UV-optical colours. Further in our study, during hot post-HB stars analysis in iur sample in section 5, we performed SED fitting (as in section 5.2 SED of HB and post-HB stars) on HB and post-HB stars of M3 and M13 using observed photometric fluxes in UVIT and HST (UBVRI) filters for the inner (outer) region of the clusters. It allows us to compute for 880 sources steallar parameters (Teff, logg, L, R, D) as in table2.dat. Objects: ---------------------------------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------------------------------- 13 42 11.62 +28 22 38.2 M 3 = BD+29 16 41 41.63 +36 27 40.7 M 13 = 2MASX J16414163+3627407 ---------------------------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 103 880 Stellar parameters along with their associated errors of 217 HBs of M3 and 678 HBs of M13 derived from SED fitting -------------------------------------------------------------------------------- See also: J/MNRAS/505/5978 : Gaia EDR3 view on Galactic globular clusters (Vasiliev+, 2021) J/MNRAS/485/3042 : UBVRI photometry in 48 globular clusters (Stetson+, 2019) J/MNRAS/482/1080 : UVIT-HST-GAIA view of NGC 288 hot stars (Sahu+, 2019) J/MNRAS/437/1609 : NGC 2808 HB stars abundances (Marino+, 2014) J/A+A/627/A34 : GC hot UV-bright stars model spectra (Moehler+, 2019) J/A+A/557/A19 : Mass and age of extreme low-mass white dwarfs (Althaus+, 2013) J/A+A/492/277 : Analysis of Collinder 69 stars with VOSA (Bayo+, 2008) J/A+A/465/249 : Age and colors of massive white dwarf stars (Althaus+, 2007) J/A+A/320/757 : M3 stars CCD photometry (Ferraro+ 1997) J/ApJ/926/99 : Above-horizontal-branch (AHB) stars in Gal. GCs (Davis+, 2022) J/ApJS/231/1 : Hot DA white dwarfs grid of synthetic spectra (Levenhagen+, 2017) J/AJ/161/204 : Astrometry and photometry for 156 ZNG UV-bright stars (Bond+, 2021) J/AJ/143/121 : UV properties of Galactic globulars with GALEX. (Schiavon+, 2012) VII/195 : Globular Clusters in the Milky Way (Harris, 1996) Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 A3 --- Cluster Cluster name parent either M3 217 times or M13 663 times (Cluster) 5- 7 A3 --- Phase Phase on CMS diagrams as fig. 2 of sect. 3 UV-optical CMDs with UVIT observed stars in bHB, iHB, and eHB regions respectively 500, 203, 177 times in our sample (Phase) 9- 12 I4 --- ID Identifier number from UVIT observations (ID) 14- 22 F9.5 deg RAdeg Right ascension (J2000) (RA) 24- 31 F8.5 deg DEdeg Declination (J2000) (DEC) 33- 37 I5 K Teff Effective temperature from SED fitting (Teff) 39- 42 I4 K E_Teff Upper uncertainty of Teff (eTeffp) 44- 47 I4 K e_Teff Lower uncertainty of Teff (eTeffm) 49- 52 F4.2 [cm/s2] logg Logaritm of the surface gravity from SED fitting (logg) 54- 57 F4.2 [cm/s2] e_logg Uncertainty of logg (elogg) 59- 64 F6.3 Lsun L Stellar luminosity from SED fitting (L) 66- 70 F5.3 Lsun e_L Uncertainty of L (eL) 72- 76 F5.3 Rsun R Stellar radius from SED fitting (R) 78- 83 F6.4 Rsun e_R Uncertainty of R (eR) 85- 97 A13 --- Model Stellar atmosphere model used (Model) (1) 99-103 F5.1 arcsec D Radial angular distance from the cluster centre from SED fitting (Radial_distance) -------------------------------------------------------------------------------- Note (1): SED fitting model used are follows: tmap2 = Tubingen NLTE Model Atmosphere Package (TMAP) Grid2, 67 occurences in our sample Kurucz2003 = Kurucz stellar atmosphere model, (Castelli, Gratton & Kurucz 1997A&A...318..841C, Castelli & Kurucz 2003IAUS..210P.A20C), 308 occurences in our sample Kurucz2003alp = Kurucz stellar atmosphere model with alp extension (Castelli, Gratton & Kurucz 1997A&A...318..841C, Castelli & Kurucz 2003IAUS..210P.A20C), 505 occurences in our sample As seen in section 5.2, the SED fitting was performed in VO SED Analyzer VOSA where we have used Kurucz stellar atmosphere model for bHB, iHB, eHB, and post-HB stars, and Tubingen NLTE Model Atmosphere Package (TMAP) Grid2 model for eHB and post-HB stars. The best-fitted model parameters including the radial distance from the cluster centre for the HB and post-HB stars are provided. -------------------------------------------------------------------------------- History: From electronic version of the journal License: CC-BY-4.0 References: Sahu et al., Paper I 2022MNRAS.514.1122S Kumar et al., Paper II This work Prabhu et al., Paper III 2022ApJ...939L..20P ================================================================================ (End) Luc Trabelsi [CDS] 19-Jun-2026