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J/ApJ/822/L5    Observed red supergiants in the inner Galaxy   (Messineo+, 2016)

Discovery of an extraordinary number of red supergiants in the inner Galaxy. Messineo M., Zhu Q., Menten K.M., Ivanov V.D., Figer D.F., Kudritzki R.-P., Rosie Chen C.-H. <Astrophys. J., 822, L5 (2016)> =2016ApJ...822L...5M (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, supergiant ; Spectra, infrared ; Equivalent widths ; Spectral types Keywords: infrared: stars - stars: evolution - supergiants Abstract: In this Letter, we present a search for Galactic red supergiant stars (RSGs) in the direction of the inner Galaxy. A total of 94 targets selected from the 2MASS (Cat. VII/233) and GLIMPSE I North (Benjamin et al. 2003, Cat. II/293; Churchwell et al. 2009PASP..121..213C) catalogs - via their blue extinction-free Q1 and Q2 colors - were spectroscopically observed at infrared wavelengths (in the H- and K-bands at R∼1000), and an extraordinary high detection rate of RSGs (>61%) was found. We identified spectroscopically 58 RSGs, based on their flat continua and large equivalent widths of the CO-band at 2.293 µm (EW>45 Å). This increase corresponds to about 25% of previously known RSGs in the Galactic region 10°<l<60°, -1.1°<b<1.1°. In order to confirm the location of the new RSGs in the inner Galaxy, distances were estimated for a subsample of 47 stars with the clump method and found to range from 3.6±0.4 to 8.6±0.7 kpc. The large new sample will allow us to investigate Galactic metallicity gradients as a function of galactocentric distances and azimuthal angles. Such information is currently an highly disputed issue to constrain models of Galaxy formation and evolution. Description: Spectroscopic observations were carried out with the Son of ISAAC (SofI; Moorwood et al. 1998Msngr..91....9M) Spectrograph on the ESO/New Technology Telescope (NTT) 3.58 m telescope of the La Silla Observatory, on the three nights from UT 2015 June 16 to 19-program ID 095.D-0252(A). Spectra with the low-resolution red grism, and the 0.6" wide slit, delivering resolution R∼980 over the wavelength range λ=1.53-2.52 µm were obtained for 94 targets. For each target a minimum number of four exposures, nodded along the slit, were taken in an ABBA sequence. Typical integration times per frame ranged from 2 to 100 s (DITsxNDITs). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 57 94 List of Observed Selected Stars
See also: VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006) II/293 : GLIMPSE Source Catalog (I + II + 3D) (IPAC 2008) J/MNRAS/427/3209 : Galactic and MC O-AGBs and RSGs stars (Jones+, 2012) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Star [1/94] Star identification number 3 A1 --- n_Star [a] Note on Star (1) 5- 6 I2 h RAh Hour of Right Ascension (J2000) 8- 9 I2 min RAm Minute of Right Ascension (J2000) 11- 15 F5.2 s RAs Second of Right Ascension (J2000) 17 A1 --- DE- Sign of the Declination (J2000) 18- 19 I2 deg DEd Degree of Declination (J2000) 21- 22 I2 arcmin DEm Arcminute of Declination (J2000) 24- 28 F5.2 arcsec DEs Arcsecond of Declination (J2000) 30- 33 F4.1 % H20 Water index percentage (H20) 35- 38 F4.1 % e_H20 Uncertainty in H20 40- 43 F4.1 0.1nm EW(CO) Equivalent width of the CO-band at 2.293µm (Å) 45- 47 F3.1 0.1nm e_EW(CO) Uncertainty in EW(CO) 49- 52 A4 --- SpType1 Spectral type derived using the relations between spectral types and EWs(CO) for red supergiants 54- 57 A4 --- SpType2 Spectral type derived using the relations between spectral types and EWs(CO) for giants
Note (1): Note as follows: a = Star 66 (2MASS J18442616-0335276) corresponds to the photometric candidate RSG A3 in Alicante 7 (Table 4 in Negueruela et al. 2011A&A...528A..59N).
History: From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 12-Feb-2018
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