J/ApJ/907/47 Composition, bright & faint Red Clump Starsin MW bulge (Lim+, 2021) ================================================================================ Difference in Chemical Composition between the Bright and Faint Red Clump Stars in the Milky Way Bulge. Lim D., Lee Y.-W., Koch A., Hong S., Johnson C.I., Kim J., Chung C., Mateo M., Bailey J.I. =2021ApJ...907...47L ================================================================================ ADC_Keywords: Milky Way; Stars, giant; Spectra, optical; Abundances, [Fe/H]; Effective temperatures; Radial velocities; Clusters, globular Keywords: Galaxy formation ; Globular star clusters ; Galaxy bulges ; Red giant clump ; Stellar abundances ; Spectroscopy Abstract: The double red clump (RC) observed in color-magnitude diagrams of the Milky Way bulge is at the heart of the current debate on the structure and formation origin of the bulge. This feature can be explained by the difference between the two RCs either in distance ("X-shaped scenario") or in chemical composition ("multiple-population scenario"). Here we report our high- resolution spectroscopy for the RC and red giant branch stars in a high-latitude field (b~-8.5{deg}) of the bulge. We find a difference in [Fe/H] between the stars in the bright and faint RC regimes, in the sense that the bright stars are enhanced in [Fe/H] with respect to the faint stars by 0.149{+/-}0.036dex. The stars on the bright RC are also enhanced in [Na/Fe] but appear to be depleted in [Al/Fe] and [O/Fe], although more observations are required to confirm the significance of these differences. Interestingly, these chemical patterns are similar to those observed among multiple stellar populations in the metal-rich bulge globular cluster Terzan 5. In addition, we find a number of Na-rich stars, which would corroborate the presence of multiple populations in the bulge. Our results support an origin of the double RC from dissolved globular clusters that harbor multiple stellar populations. Thus, our study suggests that a substantial fraction of the outer bulge stars would have originated from the assembly of such stellar systems in the early phase of the Milky Way formation. Description: The high-resolution spectra were obtained using the Michigan/Magellan Fiber System (M2FS) on the Magellan-Clay 6.5m Telescope at the Las Campanas Observatory. We used the "Hires" mode of M2FS with an order blocking filter "Bulge_GC1", which provides wavelength coverage from 6120{AA} to 6720{AA} at a spectral resolution, R~21000. The M2FS instrument can host up to 256 fibers in two spectrograph channels covering a field of view of 29.2'. However, we only used 48 fibers for observation, because a single spectrum takes six consecutive orders at our observing configuration. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 133 354 The measured atmospheric parameters and abundances -------------------------------------------------------------------------------- See also: VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006) J/ApJ/617/1091 : La and Eu abundances in 85 stars (Simmerer+, 2004) J/A+A/455/271 : Abundances of red giants in NGC 6441 (Gratton+, 2006) J/A+A/464/953 : Abundances of red giants in NGC 6441 (Gratton+, 2007) J/A+A/465/799 : Abundances of Galactic Bulge red giants (Lecureur+, 2007) J/A+A/486/437 : CN and CH line strengths in 8 Galactic GlCl (Kayser+, 2008) J/A+A/486/177 : Bulge field stars from FLAMES-GIRAFFE spectra (Zoccali+, 2008) J/A+A/505/139 : Abund. of red giants in 17 globular clusters (Carretta+, 2009) J/A+A/505/117 : Abund. of red giants in 15 globular clusters (Carretta+, 2009) J/ApJ/705/1481 : Spectroscopy of stars in 6 globular clusters (Da Costa+, 2009) J/ApJ/722/1373 : {omega} Centauri giants abundances (Johnson+, 2010) J/ApJ/721/L28 : Red clump stars in Galactic Bulge from OGLE-III (Nataf+, 2010) J/ApJ/732/108 : Abundances of 92 giants in Plaut's window (Johnson+, 2011) J/ApJ/726/L20 : Spectroscopy of Terzan 5 (Origlia+, 2011) J/AJ/142/126 : CN & CH in SDSS Galactic globular clusters (Smolinski+, 2011) J/A+A/546/A57 : Spectroscopy of 400 red giants in Bulge (Uttenthaler+, 2012) J/MNRAS/428/3660 : ARGOS line list {lambda}8395-8830{AA} (Freeman+, 2013) J/AJ/148/67 : Abundances of 156 bulge red giants (Johnson+, 2014) J/ApJ/795/22 : Iron abundance of Terzan 5 stars (Massari+, 2014) J/A+A/562/A66 : GIRAFFE Inner Bulge Survey (GIBS). I. (Zoccali+, 2014) J/ApJ/810/148 : Red giant abundances in NGC 2808 (Carretta, 2015) J/A+A/584/A46 : GIRAFFE Inner Bulge Survey (GIBS). II. (Gonzalez+, 2015) J/ApJS/216/19 : Spectroscopic HK' index for 3 globular clusters (Lim+, 2015) J/MNRAS/450/815 : Red giants in NGC 5286 (Marino+, 2015) J/A+A/587/A124 : Metal-poor stars towards the Galactic bulge (Koch+, 2016) J/ApJ/821/L25 : Bulge RRLyrae Radial Velocity Assay (BRAVA-RR) (Kunder+, 2016) J/A+A/603/L7 : 6 giants atomic data & equivalent widths (Mucciarelli+, 2017) J/MNRAS/465/501 : APOGEE N-rich stars in inner Galaxy (Schiavon+, 2017) J/MNRAS/464/2730 : M28 red giant branch stars abundances (Villanova+, 2017) J/A+A/599/A12 : Fe/H & kinematics of 26 Galactic bulge fields (Zoccali+, 2017) J/A+A/619/A134 : ATHOS Flux ratio based stellar parameterization (Hanke+, 2018) J/A+A/609/A13 : Star cluster Gaia 1 stars equivalent widths (Koch+, 2018) -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 I5 --- ID Identifier 7- 15 F9.5 deg RAdeg [274.02/274.73] Right Ascension (J2000) 17- 25 F9.5 deg DEdeg [-34.2/-33.7] Declination (J2000) 27- 31 F5.2 mag Jmag [11.7/14.5] Extinction corrected 2MASS J-band 33- 37 F5.2 mag Hmag [11/14] Extinction corrected 2MASS H-band 39- 43 F5.2 mag Kmag [10.9/13.8] Extinction corrected 2MASS K-band 45- 48 I4 K Teff [4325/5500] Effective temperature 50- 53 F4.2 [cm/s2] logg [2/4.2] log surface gravity 55- 58 F4.2 km/s Vturb [0.55/2.75] Microturbulent velocity 60- 67 F8.3 km/s RVel [-293/320] Radial velocity 69- 74 F6.3 [Sun] [Fe/H] [-1.02/0.59] Metallicity 76- 80 F5.3 [Sun] e_[Fe/H] [0.01/0.06] Uncertainty in [Fe/H] 82- 87 F6.3 [Sun] [O/Fe] [-0.31/1.21]? log O/Fe number abundance ratio 89- 94 F6.3 [Sun] [Na/Fe] [-0.36/1.06] log Na/Fe number abundance ratio 96-101 F6.3 [Sun] [Al/Fe] [-0.39/0.6]? log Al/Fe number abundance ratio 103-108 F6.3 [Sun] [Si/Fe] [-0.33/0.49] log Si/Fe number abundance ratio 110-115 F6.3 [Sun] [Ca/Fe] [-0.49/0.69] log Ca/Fe number abundance ratio 117-122 F6.3 [Sun] [Cr/Fe] [-0.59/1.1]? log Cr/Fe number abundance ratio 124-129 F6.3 [Sun] [Ni/Fe] [-0.28/0.53]? log Ni/Fe number abundance ratio 131-133 A3 --- Group Group type (1) -------------------------------------------------------------------------------- Note (1): Groups as follows: RGB = Red Giant Branch (24 occurrences) Twi = Twilight zone (31 occurrences) bRC = bright Red Clump (135 occurrences) fRC = faint Red Clump (164 occurrences) -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Coralie Fix [CDS], 01-Jun-2022