Emission-line stars in M31 from the SPLASH and PHAT surveys

Abstract

We present a sample of 224 stars that emit H$\alpha$ (H$\alpha$ stars) in the Andromeda galaxy (M31). The stars were selected from $\sim$ 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 H$\alpha$ stars. We identified five distinct categories of H$\alpha$ 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 $\sim$ 12 per cent of B-type stars exhibit H$\alpha$ 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 H$\alpha$ stars are Be stars evolving off the MS with fading H$\alpha$ emission. We separated RHeB from AGB H$\alpha$ stars. We conclude that the 61 RHeB and AGB stars are likely to be Long Period Variables. We found that $\sim$ 14 per cent of C-rich AGB stars (C stars) emit H$\alpha$, which is an upper limit for the ratio of C-rich Miras to C stars. This catalogue of H$\alpha$ stars will be useful to constrain stellar evolutionary models, calibrate distance indicators for intermediate age populations, and investigate the properties of M31.

arXiv commentAccepted for publication in MNRAS. 25 pages, 14 figures

References in corpus (34)

• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Astrophysics Source Code Library
• The DEEP2 Galaxy Redshift Survey: Design, Observations, Data Reduction, and Redshifts
• A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
• A catalogue of symbiotic stars
• The Panchromatic Hubble Andromeda Treasury
• The Panchromatic Hubble Andromeda Treasury X. Ultraviolet to Infrared Photometry of 117 Million Equidistant Stars
• Parameterising the third dredge-up in asymptotic giant branch stars
• Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams
• The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31)
• Asymptotic Giant Branch evolution at varying surface C/O ratio: effects of changes in molecular opacities
• The Detailed Star Formation History in the Spheroid, Outer Disk, and Tidal Stream of the Andromeda Galaxy
• Surveying the Agents of Galaxy Evolution in the Tidally-Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC) II. Cool Evolved Stars
• Chemical abundances in M31 from HII regions
• The Panchromatic Hubble Andromeda Treasury XI: The Spatially-Resolved Recent Star Formation History of M31
• Effects of metallicity, star-formation conditions, and evolution in B and Be stars. II: Small Magellanic Cloud, field of NGC 330
• Helium enrichment and Carbon-star Production in Metal-rich Populations
• AGB stars in the Magellanic Clouds. I. The C/M ratio
• Dust driven mass loss from carbon stars as a function of stellar parameters - I. A grid of Solar-metallicity wind models
• The Role of Evolutionary Age and Metallicity in the Formation of Classical Be Circumstellar Disks I. New Candidate Be Stars in the LMC, SMC, and Milky Way
• Variability and spectral classification of LMC giants: results from DENIS and EROS
• The Contribution of TP-AGB and RHeB Stars to the Near-IR Luminosity of Local Galaxies: Implications for Stellar Mass Measurements of High Redshift Galaxies
• A clear age-velocity dispersion correlation in Andromeda's stellar disk
• Evolution of Thermally Pulsing Asymptotic Giant Branch Stars V: Constraining the Mass Loss and Lifetimes of Intermediate Mass, Low Metallicity AGB Stars
• Symbiotic stars and other Halpha emission line stars towards the Galactic Bulge
• Observational Constraints on Red and Blue Helium Burning Sequences
• The SPLASH Survey: Kinematics of Andromeda's Inner Spheroid
• AGB stars as tracers of metallicity and mean age across M33
• Panchromatic Hubble Andromeda Treasury XII. Mapping Stellar Metallicity Distributions in M31
• Emission-line stars discovered in the UKST H-alpha survey of the Large Magellanic Cloud; Part 1: Hot stars
• Asymptotic Giant Branch Variables in the Galaxy and the Local Group
• A Spectroscopic and Photometric Exploration of the C/M Ratio in the Disk of M31
• Cool carbon stars in the halo and in dwarf galaxies: Halpha, colours, and variabiity
• Measuring The Mass Loss Evolution at The Tip of The Asymptotic Giant Branch

Cited by in corpus (2)

• A Census of Thermally-Pulsing AGB stars in the Andromeda Galaxy and a First Estimate of their Contribution to the Global Dust Budget
• The Hubble Space Telescope Advanced Camera for Surveys Emission Line Survey of Andromeda. I: Classical Be Stars