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J/ApJ/838/83  Radial velocities, abundances & membership in TriII (Kirby+, 2017)

Triangulum II. Not especially dense after all. Kirby E.N., Cohen J.G., Simon J.D., Guhathakurta P., Thygesen A.O., Duggan G.E. <Astrophys. J., 838, 83-83 (2017)> =2017ApJ...838...83K (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Radial velocities ; Velocity dispersion ; Equivalent widths ; Photometry, SDSS ; Galaxies, nearby Keywords: galaxies: abundances; galaxies: dwarf; Local Group Abstract: Among the Milky Way satellites discovered in the past three years, Triangulum II has presented the most difficulty in revealing its dynamical status. Kirby+ (2015ApJ...814L...7K) identified it as the most dark-matter-dominated galaxy known, with a mass-to-light ratio within the half-light radius of 3600-2100+3500M/L. On the other hand, Martin+ (2016ApJ...818...40M) measured an outer velocity dispersion that is 3.5±2.1 times larger than the central velocity dispersion, suggesting that the system might not be in equilibrium. From new multi-epoch Keck/DEIMOS measurements of 13 member stars in Triangulum II, we constrain the velocity dispersion to be σv<3.4km/s (90%C.L.). Our previous measurement of σv, based on six stars, was inflated by the presence of a binary star with variable radial velocity. We find no evidence that the velocity dispersion increases with radius. The stars display a wide range of metallicities, indicating that Triangulum II retained supernova ejecta and therefore possesses, or once possessed, a massive dark matter halo. However, the detection of a metallicity dispersion hinges on the membership of the two most metal-rich stars. The stellar mass is lower than galaxies of similar mean stellar metallicity, which might indicate that Triangulum II is either a star cluster or a tidally stripped dwarf galaxy. Detailed abundances of one star show heavily depressed neutron-capture abundances, similar to stars in most other ultra-faint dwarf galaxies but unlike stars in globular clusters. Description: Observations were obtained with the Deep Extragalactic Imaging Multi-Object Spectrograph (DEIMOS) medium-resolution spectrograph at the Nasmyth focus of the Keck II telescope on five different dates spanning 2015 Oct to 2016 Sep. This 1200G grating provided a spectral resolving power of R=7000 at 8500Å. We obtained Keck/HIRES spectra of star 40, the brightest known member of Tri II, on 2016 August 25 (spectral resolving power of R=49000 over the spectral range of 3933-8374Å). Objects: ---------------------------------------------------------------------------- RA (ICRS) DE Designation(s) (HRV) ---------------------------------------------------------------------------- 02 13 17.40 +36 10 42.4 Triangulum II = NAME Triangulum II (-382km/s) 02 13 16.54 +36 10 45.7 TriII 40 = [MIC2016] 40 (-382km/s) ---------------------------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 93 34 Radial velocities table4.dat 93 6 Chemical abundances table5.dat 41 167 *Line list with equivalent widths of [MIC2016] 40; from erratum published in 2017, ApJ, 839, 135
Note on table5.dat: These summary data are provided for the reader's information, but the abundances were actually computed with Cohen et al.'s (2004ApJ...612.1107C) longer hyperfine line lists.
See also: J/A+A/287/927 : Abundances for lines of n-capture in 19 stars (Gratton+ 1994) J/AJ/120/1841 : Abundances & Kinematics of Halo & Disk Stars (Fulbright 2000) J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004) J/AJ/131/2114 : Radial velocities in Fornax dSph (Walker+, 2006) J/ApJ/663/960 : Radial velocities of Leo I stars (Sohn+, 2007) J/ApJ/682/1217 : Abundances in red giants in 7 globular clusters (Kirby+, 2008) J/ApJ/692/1464 : Spectroscopy of Segue 1 (Geha+, 2009) J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009) J/ApJ/708/560 : Spectroscopy of UMa II and Coma Ber (Frebel+, 2010) J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010) J/ApJ/740/60 : EWs for NGC2419 and NGC7099 RGB stars (Cohen+, 2011) J/ApJ/736/146 : Radial velocities of stars in Bootes I (Koposov+, 2011) J/ApJ/733/46 : Velocity measurements in Segue 1 (Simon+, 2011) J/ApJ/760/86 : Equivalent widths for 13 NGC2419 RGB stars (Cohen+, 2012) J/AJ/144/168 : Spectroscopy of Scl 1019417 and UMi 20103 (Kirby+, 2012) J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012) J/ApJ/750/99 : The Pan-STARRS1 photometric system (Tonry+, 2012) J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013) J/ApJ/770/16 : Spectroscopic members of Segue 2 galaxy (Kirby+, 2013) J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013) J/ApJ/767/134 : Abundances of red giant stars in UFD galaxies (Vargas+, 2013) J/ApJ/786/74 : EW measurements of 6 Segue 1 red giants (Frebel+, 2014) J/ApJ/801/125 : Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015) J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015) J/ApJ/830/93 : Ret II brightest red giant members abundances (Ji+, 2016) J/ApJ/817/41 : Abundances of 4 metal-poor red giants in BooII (Ji+, 2016) J/ApJ/819/135 : Lithium-rich giants in globular clusters (Kirby+, 2016) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 3 I3 --- [KCS2015] [45/177]? Identifier from Kirby+ (2015ApJ...814L...7K) 5- 6 I2 --- [MIC2016] [1/50]? Identifier from Martin+ (2016ApJ...818...40M) 8- 10 A3 --- f_[MIC2016] [a,h ] Flag(s) on Star (1) 12- 13 I2 h RAh [2] Hour of Right Ascension (J2000) 15- 16 I2 min RAm [12/13] Minute of Right Ascension (J2000) 18- 22 F5.2 s RAs Second of Right Ascension (J2000) 24 A1 --- DE- [+] Sign of the Declination (J2000) 25- 26 I2 deg DEd [36] Degree of Declination (J2000) 28- 29 I2 arcmin DEm [5/16] Arcminute of Declination (J2000) 31- 34 F4.1 arcsec DEs Arcsecond of Declination (J2000) 36- 39 F4.2 arcmin Rad [0.1/8.3] Radius 41- 45 F5.2 mag gP1mag [17/22] Pan-STARRS-1 g mag photometry (2) 47- 50 F4.2 mag e_gP1mag [0/0.2] Uncertainty for gP1mag 52- 56 F5.2 mag iP1mag [16.3/21.7] Pan-STARRS-1 i mag photometry (2) 58- 61 F4.2 mag e_iP1mag [0/0.2] Uncertainty for iP1mag 63- 67 A5 --- Masks [ b-g] Slit Mask identifier(s) (3) 69- 73 F5.1 --- S/N [14/220] Signal-to-noise ratio in Å-1 (4) 75- 80 F6.1 km/s HRV [-388/11]? Heliocentric radial velocity 82- 85 F4.1 km/s e_HRV [1.5/18]? Uncertainty in HRV 87- 89 F3.1 km/s sigma [0.1/3]? Velocity dispersion σ(ν) 91 A1 --- Mm Member status (Y: 13 sources; N: 20 sources) 93 A1 --- f_Mm [b] Flag on M16 25 (5)
Note (1): Flag as follows: a = one of the six stars for which it was possible to measure abundances h = Star 40 was also observed with Keck/HIRES; see text and the "Description" section above. Note (2): gi photometry is from the Pan-STARRS-1 observations by Martin+ (2016ApJ...818...40M). Note (3): Slit Mask identifier from table 1 (DEIMOS observations): --------------------------------------------------------------------- Slitmask Targets UT date Airmass Seeing Exposures Exp. Time (arcsec) (s) --------------------------------------------------------------------- TriIIb* 29 2015 Oct 8 1.4 0.9 3 3120 TriIIc 25 2015 Dec 14 1.1 0.9 4 7200 TriIId 28 2016 Jan 29 1.1 0.9 4 5100 TriIIe 25 2016 Jan 29 1.3 1.1 3 4803 TriIIf 21 2016 Jun 29 1.6 1.0 2 2700 TriIIg 27 2016 Sep 7 1.1 0.7 3 3060 --------------------------------------------------------------------- *: Observations by Kirby+, 2015ApJ...814L...7K Note (4): To convert to S/N per pixel, multiply by 0.57. Note (5): b = M16 25 is a double-lined spectroscopic binary. The velocities of the individual components straddle the mean radial velocity of Tri II, but the two epochs were not sufficient to measure the center-of-mass velocity reliably.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 3 I3 --- [KCS2015] [65/128]? Identification number from Kirby+ (2015ApJ...814L...7K) 5- 6 I2 --- [MIC2016] [20/46]? Identification number from Martin+ (2016ApJ...818...40M) 8- 11 I4 K Teff [4917/5635] Effective temperature 13- 16 F4.2 [cm/s2] logg [1.8/3.5] Log surface gravity 18- 22 F5.2 [-] [Fe/H]CaT [-3.2/-0.9] Metallicity from the Ca triplet 24- 27 F4.2 [-] e_[Fe/H]CaT [0.02/0.2] [Fe/H]CaT uncertainty 29- 33 F5.2 [-] [Fe/H] [-3/-1.4] [Fe/H] abundance 35- 38 F4.2 [-] e_[Fe/H] [0.1/0.3] [Fe/H] uncertainty 40- 44 F5.2 [-] [Mg/Fe] [0.2/1.1]? [Mg/Fe] abundance 46- 49 F4.2 [-] e_[Mg/Fe] [0.2/0.9]? [Mg/Fe] uncertainty 51- 55 F5.2 [-] [Si/Fe] [-0.09/0.6]? [Si/Fe] abundance 57- 60 F4.2 [-] e_[Si/Fe] [0.1/0.5]? [Si/Fe] uncertainty 62- 66 F5.2 [-] [Ca/Fe] [-0.4/0.5] [Ca/Fe] abundance 68- 71 F4.2 [-] e_[Ca/Fe] [0.1/0.9] [Ca/Fe] uncertainty 73- 77 F5.2 [-] [Ti/Fe] [-0.8/1]? [Ti/Fe] abundance 79- 82 F4.2 [-] e_[Ti/Fe] [0.1/0.8]? [Ti/Fe] uncertainty 84- 88 F5.2 [-] [a/Fe] [-0.5/0.5] [α/Fe] abundance 90- 93 F4.2 [-] e_[a/Fe] [0.1/0.36] [a/Fe] uncertainty
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1- 5 A5 --- Ion Ion 7- 14 F8.3 0.1nm lamAir [3949.9/7699] Wavelength in air, in Å units (1) 16- 20 F5.3 eV ExPot [0/5.7] Excitation potential 22- 27 F6.3 [-] loggf [-9.8/0.7] Logarithm of oscillator strength (2) 29 A1 --- l_EW Upper limit flag on EW 30- 34 F5.1 0.1pm EW [4/287] Equivalent width 36 A1 --- l_eps Upper limit flag on eps 37- 41 F5.2 [Sun] eps [-3.2/6.8] Abundance derived from this line, unitless relative to Sun
Note (1): The average wavelengths of the absorption lines in each hyperfine complex. Note (2): The oscillator strengths are the sum of the individual hyperfine oscillator strengths.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Oct-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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