J/MNRAS/465/4180    Hα stars in M31 HST photometry       (Prichard+, 2017)

Emission-line stars in M31 from the SPLASH and PHAT surveys. Prichard L.J., Guhathakurta P., Hamren K.M., Dalcanton J.J., Dorman C.E., Seth A.C., Williams B.F., Damon G.A., Ilango A., Ilango M. <Mon. Not. R. Astron. Soc., 465, 4180-4203 (2017)> =2017MNRAS.465.4180P 2017MNRAS.465.4180P (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, emission ; Photometry, HST ; Radial velocities Keywords: surveys - stars: AGB and post-AGB - stars: emission-line - Be, stars: variables: general - Local Group - galaxies: stellar content Abstract: We present a sample of 224 stars that emit Hα (Hα stars) in the Andromeda galaxy (M31). The stars were selected from ∼5000 spectra, collected as part of the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey using Keck II/DEIMOS. We used six-filter Hubble Space Telescope photometry from the Panchromatic Hubble Andromeda Treasury survey to classify and investigate the properties of the Hα stars. We identified five distinct categories of Hα star: B-type main-sequence (MS) stars, 'transitioning'-MS (T-MS) stars, red core He burning (RHeB) stars, non-C-rich asymptotic giant branch (AGB) stars, and C-rich AGB stars. We found that ∼12 per cent of B-type stars exhibit Hα emission (Be stars). The frequency of Be to all B stars is known to vary with the metallicity of their environment. Comparing this proportion of Be stars with other environments around the Local Group, the result could indicate that M31 is more metal-rich than the Milky Way. We predict that the 17 T-MS Hα stars are Be stars evolving off the MS with fading Hα emission. We separated RHeB from AGB Hα stars. We conclude that the 61 RHeB and AGB stars are likely to be long-period variables. We found that ∼14 per cent of C-rich AGB stars (C stars) emit Hα, which is an upper limit for the ratio of C-rich Miras to C stars. This catalogue of Hα stars will be useful to constrain stellar evolutionary models, calibrate distance indicators for intermediate-age populations, and investigate the properties of M31. Description: The PHAT survey is a multicycle HST programme. The survey covers around a third of M31's disc in six filters that span from ultraviolet (UV) to near-infrared (NIR). With HST's observing capabilities, the disc of M31, out to 20kpc, is resolved into more than 100 million stars. Dalcanton et al. (2012ApJS..200...18D 2012ApJS..200...18D) chose to observe the northeast quadrant of M31 as it has the least obscured active star-forming regions and least extinction. The spatial coverage selected by the PHAT team also maximized the range of environments and thus stellar evolutionary stages observed. They used two UV filters (F275W and F336W), one optical filter (F475W), one far-red filter (F814W), and two NIR filters (F110W and F160W). The filters were chosen to constrain extinction and effective temperature of a range of stellar populations. To select Hα stars, we used a spectroscopic sample that was collected as part of the SPLASH survey. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file tablea1.dat 201 224 List of selected Hα stars -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 I5 --- Index Index 7- 38 A32 --- Fullname Name of the spectrum fits file 40- 49 A10 --- Name Object name 51- 56 A6 --- Class Classification 58- 62 A5 --- Mask DEIMOS mask name 64- 66 A3 --- Slit Mask slit number 68- 72 F5.1 mm-1 Grate [600] Grate 74- 75 I2 h RAh Right ascension (J2000) 77- 78 I2 min RAm Right ascension (J2000) 80- 85 F6.3 s RAs Right ascension (J2000) 87 A1 --- DE- Declination sign (J2000) 88- 89 I2 deg DEd Declination (J2000) 91- 92 I2 arcmin DEm Declination (J2000) 94- 99 F6.3 arcsec DEs Declination (J2000) 100-119 F20.16 0.1nm EW Hα equivalent width 121-141 F21.18 0.1nm e_EW rms uncertainty on EW 143-145 I3 km/s sigma Velocity dispersion 147-148 I2 km/s e_sigma rms uncertainty on sigma 150-155 F6.1 km/s HV Heliocentric velocity 157-161 F5.2 kpc Rdp Deprojected radius 163-168 F6.2 mag F275W ?=100 PHAT HST F275W magnitude (UV) 170-175 F6.2 mag F336W ?=100 PHAT HST F336W magnitude (UV) 177-181 F5.2 mag F475W ?=100 PHAT HST F475W magnitude (optical) 183-187 F5.2 mag F814W ?=100 PHAT HST F814W magnitude (far-red) 189-194 F6.2 mag F110W ?=100 PHAT HST F110W magnitude (NIR) 196-201 F6.2 mag F160W ?=100 PHAT HST F160W magnitude (NIR) -------------------------------------------------------------------------------- History: From electronic version of the journal
(End) Patricia Vannier [CDS] 20-Dec-2018
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