J/ApJ/852/99 Abundances of 3 metal-poor stars in Horologium I (Nagasawa+, 2018)
Chemical abundance analysis of three α-poor, metal-poor stars in the
ultrafaint dwarf galaxy Horologium I.
Nagasawa D.Q., Marshall J.L., Li T.S., Hansen T.T., Simon J.D.,
Bernstein R.A., Balbinot E., Drlica-Wagner A., Pace A.B., Strigari L.E.,
Pellegrino C.M., DePoy D.L., Suntzeff N.B., Bechtol K., Walker A.R.,
Abbott T.M.C., Abdalla F.B., Allam S., Annis J., Benoit-Levy A., Bertin E.,
Brooks D., Carnero Rosell A., Carrasco Kind M., Carretero J., Cunha C.E.,
D'Andrea C.B., da Costa L.N., Davis C., Desai S., Doel P., Eifler T.F.,
Flaugher B., Fosalba P., Frieman J., Garcia-Bellido J., Gaztanaga E.,
Gerdes D.W., Gruen D., Gruendl R.A., Gschwend J., Gutierrez G.,
Hartley W.G., Honscheid K., James D.J., Jeltema T., Krause E., Kuehn K.,
Kuhlmann S., Kuropatkin N., March M., Miquel R., Nord B., Roodman A.,
Sanchez E., Santiago B., Scarpine V., Schindler R., Schubnell M.,
Sevilla-Noarbe I., Smith M., Smith R.C., Soares-Santos M., Sobreira F.,
Suchyta E., Tarle G., Thomas D., Tucker D.L., Wechsler R.H., Wolf R.C.,
Yanny B.
<Astrophys. J., 852, 99 (2018)>
=2018ApJ...852...99N 2018ApJ...852...99N
ADC_Keywords: Abundances; Galaxies, spectra; Stars, metal-deficient
Keywords: galaxies: abundances ; galaxies: dwarf ; stars: abundances ;
stars: chemically peculiar
Abstract:
We present chemical abundance measurements of three stars in the
ultrafaint dwarf galaxy Horologium I, a Milky Way satellite discovered
by the Dark Energy Survey. Using high-resolution spectroscopic
observations, we measure the metallicity of the three stars, as well
as abundance ratios of several α-elements, iron-peak elements,
and neutron-capture elements. The abundance pattern is relatively
consistent among all three stars, which have a low average metallicity
of [Fe/H]~-2.6 and are not α-enhanced ([α/Fe]∼0.0). This
result is unexpected when compared to other low-metallicity stars in
the Galactic halo and other ultrafaint dwarfs and suggests the
possibility of a different mechanism for the enrichment of Hor I
compared to other satellites. We discuss possible scenarios that could
lead to this observed nucleosynthetic signature, including extended
star formation, enrichment by a Population III supernova, and or an
association with the Large Magellanic Cloud.
Description:
Observations were performed using the FLAMES-UVES spectrograph on the
VLT in Paranal, Chile, as part of program 096.D-0967(B) (PI: E. Balbinot)
and the MIKE spectrograph at the Magellan-Clay Telescope at Las
Campanas Observatory (PI: R. Bernstein).
UVES observations took place on five nights over the months of 2015
December to 2016 January in 14 40-minute exposures. See section 2.1.1.
MIKE observations of DES J025535-540643, a confirmed Hor I member star
(Koposov+ 2015ApJ...811...62K 2015ApJ...811...62K), took place on 2016 August 06 in five
30-minute exposures. See section 2.1.2.
In Figure 1 we present a color-magnitude diagram of the confirmed
(Koposov+ 2015ApJ...811...62K 2015ApJ...811...62K) and high-probability (Bechtol+
2015ApJ...807...50B 2015ApJ...807...50B) member stars of Hor I, constructed using
photometry from the Dark Energy Survey (DES; the Dark Energy Survey
Collaboration 2005astro.ph.10346T 2005astro.ph.10346T).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 69 3 DES astrometry and photometry of three member
stars of Hor I
table2.dat 39 3 Observing details
table3.dat 28 190 Atomic line data
table4.dat 65 3 Measured stellar parameters
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See also:
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/ApJS/167/292 : Transition probabilities for Gd II (Den Hartog+, 2006)
J/ApJS/162/227 : Transition probabilities for SmII (Lawler+, 2006)
J/ApJ/667/1267 : CrI transition probabilities (Sobeck+, 2007)
J/AJ/135/1580 : Element abundances in ten red giants of Car dSph (Koch+, 2008)
J/AJ/135/209 : Rotational and RVs 761 HIP giants (Massarotti+, 2008)
J/A+A/480/379 : Abundances of 59 red giants in LMC (Pompeia+, 2008)
J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009)
J/ApJS/182/51 : Transition prob. of rare earth elements (Lawler+, 2009)
J/ApJS/182/80 : Rare earth abundances (Sneden+, 2009)
J/AN/331/474 : Abundances of metal-poor stars (Frebel, 2010)
J/ApJ/708/560 : Spectroscopy of UMa II and Coma Ber (Frebel+, 2010)
J/ApJ/724/341 : Nucleosynthesis of massive metal-free stars (Heger+, 2010)
J/ApJ/723/1632 : Abundance spreads in Bootes I and Segue 1 (Norris+, 2010)
J/ApJS/194/35 : Atomic transition probabilities of Mn (Den Hartog+, 2011)
J/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)
J/AJ/144/88 : Spectrosc. of 6 LMC RR Lyrae & 3 SMC RR Lyrae (Haschke+, 2012)
J/ApJ/761/33 : Chemical data of 89 stars in the LMC disk (Lapenna+, 2012)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013)
J/ApJ/763/61 : Abundances of 7 red giant members of BootesI (Gilmore+, 2013)
J/A+A/560/A44 : Abundances of LMC bar and disk stars (Van der Swaelmen+, 2013)
J/ApJ/767/134 : Abundances of red giant stars in UFD galaxies (Vargas+, 2013)
J/ApJ/762/26 : Most metal-poor stars. II. Galactic halo stars (Yong+, 2013)
J/ApJ/786/74 : EW measurements of 6 Segue 1 red giants (Frebel+, 2014)
J/A+A/562/A146 : Chemical abundances of 8 metal-poor stars (Ishigaki+, 2014)
J/ApJS/215/20 : Vanadium log(gf) and transition probabilities (Lawler+, 2014)
J/A+A/571/A47 : Extensive linelist of CH in stellar atm. (Masseron+, 2014)
J/MNRAS/440/2665 : SDSS J021933.13+200830.2 spectroscopy (Roederer+, 2014)
J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014)
J/MNRAS/441/3127 : FeI oscillator strengths for Gaia-ESO (Ruffoni+, 2014)
J/ApJS/214/26 : Line lists for CN isotopes transitions (Sneden+, 2014)
J/ApJS/211/20 : NiI transition probability measurements (Wood+, 2014)
J/ApJ/803/63 : gr photometry of stars in Kim 2 (Kim+, 2015)
J/ApJS/220/13 : Co I transition probabilities (Lawler+, 2015)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/ApJ/802/93 : Abundance analysis of 5 stars in Sculptor (Simon+, 2015)
J/ApJ/826/110 : Boo-127 and Boo-980 high-resolution spectra (Frebel+, 2016)
J/ApJ/830/93 : Abundances of Ret II brightest red giant members (Ji+, 2016)
J/ApJ/817/41 : Abundances of 4 metal-poor red giants in BooII (Ji+, 2016)
J/AJ/151/82 : 4 brightest red giants in Ret 2 (Roederer+, 2016)
J/ApJ/817/53 : Fe-group elemental abundances in HD84937 (Sneden+, 2016)
J/ApJ/819/53 : Magellan/M2FS spectrosc. of Tucana 2 & Grus 1 (Walker+, 2016)
J/ApJ/838/44 : Abundances of the brightest member of Tuc III (Hansen+, 2017)
J/ApJ/838/83 : RVs, abundances & membership in TriII (Kirby+, 2017)
J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [DES]
5- 18 A14 --- DES DES identifier (JHHMMSS+DDMMSS)
19 A1 --- f_DES Flag on DES (1)
21- 28 F8.5 deg RAdeg [43.8/44] Right ascension in decimal degrees (J2000)
30- 38 F9.5 deg DEdeg [-54.2/-54] Declination in decimal degrees (J2000)
40- 44 F5.2 mag gmag [17.7/18.7] DES g-band magnitude
45 A1 --- f_gmag Flag on gmag (1)
47- 51 F5.2 mag rmag [16.7/18] DES r-band magnitude
53- 57 F5.2 mag imag [16.3/17.7] DES i-band magnitude
59- 63 F5.2 mag zmag [16.1/17.6] DES z-band magnitude
65- 69 F5.2 mag Ymag [16.1/17.5] DES Y-band magnitude
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Note (1): Flag as follows:
a = Referred to as Horo 9 by Koposov+ (2015ApJ...811...62K 2015ApJ...811...62K).
b = Referred to as Horo 10 by Koposov+ (2015ApJ...811...62K 2015ApJ...811...62K).
c = Note that Koposov+ (2015ApJ...811...62) report g=19.31mag for this star.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [DES]
5- 18 A14 --- DES DES identifier (JHHMMSS+DDMMSS)
20- 23 A4 --- Inst Instrument
25- 26 I2 --- S/N5300 [20/35] Signal to noise ration at 5300_Å
28- 29 I2 --- S/N6300 [20/40] Signal to noise ration at 6300_Å
31- 35 F5.1 km/s HRV [114.3/118.6] Heliocentric velocity
37- 39 F3.1 km/s e_HRV [0.5/0.6] HRV uncertainty
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Ion Species (1)
7- 13 F7.2 0.1nm lambda [3818.7/8688.7] Wavelength in Angstroms
15- 18 F4.2 eV ExPot [0/5.7]? Excitation potential (1)
20- 25 F6.2 [-] log(gf) [-10.6/0.7]? Log of degeneracy times oscillator
strength (1)
27- 28 I2 --- Ref [1/30] Literature reference (2)
--------------------------------------------------------------------------------
Note (1): The CH and CN are molecular bands and thus have no ExPot and log(gf)
values. These are left blank.
Note (2): Reference as follows:
1 = Kurucz (2011CaJPh..89..417K 2011CaJPh..89..417K);
2 = Kramida, Ralchenko & Reader (2016, NIST Atomic Spectra Database
(version 5.4) http://physics.nist.gov/asd);
3 = Ruffoni et al. (2014, J/MNRAS/441/3127);
4 = Masseron et al. (2014, J/A+A/571/A47)
5 = Sneden et al. (2014, J/ApJS/214/26);
6 = Lawler & Dakin (1989JOSAB...6.1457L 1989JOSAB...6.1457L) with hfs from
Kurucz & Bell (1995KurCD..23.....K 1995KurCD..23.....K)
7 = Lawler et al. (2013ApJS..205...11L 2013ApJS..205...11L)
8 = Lawler et al. (2014, J/ApJS/215/20);
9 = Sobeck et al. (2007, J/ApJ/667/1267);
10 = Den Hartog et al. (2011, J/ApJS/194/35);
11 = Lawler et al. (2015, J/ApJS/220/13);
12 = Wood et al. (2014, J/ApJS/211/20);
13 = Kurucz & Bell (1995KurCD..23.....K 1995KurCD..23.....K)
14 = Biemont et al. (2011AIPC.1344...31B 2011AIPC.1344...31B)
15 = Biemont et al. (1981ApJ...248..867B 1981ApJ...248..867B)
16 = Palmeri et al. (2005MNRAS.363..452P 2005MNRAS.363..452P)
17 = Wickliffe et al. (1994JQSRT..51..545W 1994JQSRT..51..545W)
18 = Gallagher et al. (2010A&A...523A..24G 2010A&A...523A..24G)
19 = Gallagher (2012PhDT.......276G 2012PhDT.......276G)
20 = Lawler et al. (2001ApJ...556..452L 2001ApJ...556..452L)
21 = Lawler et al. (2009ApJS..182...51L 2009ApJS..182...51L)
22 = Li et al. (2007PhyS...76..577L 2007PhyS...76..577L) with hfs from
Sneden et al. (2009, J/ApJS/182/80);
23 = Den Hartog et al. (2003ApJS..148..543D 2003ApJS..148..543D)
24 = Lawler et al. (2006, J/ApJS/162/227);
25 = Lawler et al. (2001ApJ...563.1075L 2001ApJ...563.1075L)
26 = Den Hartog et al. (2006, J/ApJS/167/292);
27 = Lawler et al. (2001ApJS..137..341L 2001ApJS..137..341L) with hfs from
Lawler et al. (2001ApJS..137..351L 2001ApJS..137..351L)
28 = Lawler et al. (2001ApJS..137..341L 2001ApJS..137..341L)
29 = Wickliffe et al. (2000JQSRT..66..363W 2000JQSRT..66..363W)
30 = Lawler et al. (2011ApJS..178...71L 2011ApJS..178...71L).
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [DES]
5- 18 A14 --- DES DES identifier (JHHMMSS+DDMMSS)
20- 23 I4 K Teff [4500/5000] Effective temperature
25- 27 I3 K e_Teff [100] Teff uncertainty
29- 31 F3.1 [cm/s2] logg [1.4/2] Log of surface gravity
33- 35 F3.1 [cm/s2] e_logg [0.2] logg uncertainty
37- 39 F3.1 km/s Vt [0.8/3.5] Microturbulent velocity
41- 43 F3.1 km/s e_Vt [0.5] Vt uncertainty
45- 49 F5.2 [Sun] [Fe/H] [-2.9/-2.4] Metallicity
51- 54 F4.2 [Sun] e_[Fe/H] [0.1/0.2] Metallicity uncertainty
56- 60 F5.2 [Sun] [Ca/Fe] [-0.07/0] Abundance of [Ca/Fe]
62- 65 F4.2 [Sun] e_[Ca/Fe] [0.1/0.3] Abundance of [Ca/Fe] uncertainty
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 19-Sep-2018