J/MNRAS/449/761 EWs of metal-poor stars in the UMi I dSph galaxy (Ural+, 2015)
An inefficient dwarf: chemical abundances and the evolution of the Ursa Minor
dwarf spheroidal galaxy.
Ural U., Cescutti G., Koch A., Kleyna J., Feltzing S., Wilkinson M.I.
<Mon. Not. R. Astron. Soc., 449, 761-770 (2015)>
=2015MNRAS.449..761U 2015MNRAS.449..761U (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, metal-deficient ; Equivalent widths
Keywords: galaxies: abundances - galaxies: dwarf - galaxies: evolution -
galaxies: individual: UMi I dSph - Local Group
Abstract:
We present detailed chemical element abundance ratios of 17 elements
with eight≤Z≤60 in three metal-poor stars in the Ursa Minor dwarf
spheroidal galaxy, which we combine with extant data from the literature
to assess the predictions of a novel suite of galaxy chemical
evolution models. The spectroscopic data were obtained with the
Keck/High-Resolution Echelle Spectrograph instrument and revealed low
metallicities of [Fe/H]=-2.12, -2.13 and -2.67 dex. While the most
metal-poor star in our sample shows an overabundance of [Mn/Fe] and
other Fe-peak elements, our overall findings are in agreement with
previous studies of this galaxy: elevated values of the [α/Fe]
ratios that are similar to, or only slightly lower than, the halo values
but with SN Ia enrichment at very low metallicity, as well as an
enhancement of the ratio of first to second peak neutron capture elements
[Y/Ba] with decreasing metallicity. The chemical evolution models which
were tailored to reproduce the metallicity distribution function of
the dwarf spheroidal, indicate that Ursa Minor had an extended star
formation which lasted nearly 5 Gyr with low efficiency and are able
to explain the [Y/Ba] enhancement at low metallicity for the first time.
In particular, we show that the present-day lack of gas is probably
due to continuous loss of gas from the system, which we model as winds.
Description:
The observations were made using the High-Resolution Echelle Spectrograph
(HIRES; Vogt, Allen & Bigelow 1994SPIE.2198..362V 1994SPIE.2198..362V) on the Keck telescope
on the night of UT 2006-06-05. The targets were selected from legacy
Kitt Peak National Observatory (KPNO) 4 m mosaic imaging as in Wilkinson,
Kleyna & Evans (2004ApJ...611L..21W 2004ApJ...611L..21W).
Objects:
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RA (ICRS) DE Designation(s)
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15 09 11.34 +67 12 51.7 UMi I dSph = NAME UMi Galaxy
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 81 3 Observed stars
table2.dat 43 343 Equivalent width measurements
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See also:
J/AJ/90/2221 : UMi dwarf galaxy BV photometry (Olszewski+, 1985)
J/AJ/110/2131 : M/L for Draco and UMi. I. (Armandroff+ 1995)
J/AJ/124/3222 : VI photometry of Draco and UMi galaxies (Bellazzini+, 2002)
J/AJ/125/1352 : Ursa Minor dSph M,T2, DDO51 photometry (Palma+, 2003)
J/ApJ/617/L41 : Red giant variable candidates in UMi dSph (Mighell+, 2004)
J/ApJ/719/931 : Chemical evolution of the UMi dSph (Cohen+, 2010)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Star Target star name (UMINNN)
8- 12 F5.2 mag Imag Johnson-Cousins I-band magnitude from
Kleyna et al. (1998AJ....115.2359K 1998AJ....115.2359K)
14- 18 F5.2 mag Vmag Johnson-Cousins V-band magnitude from
Kleyna et al. (1998AJ....115.2359K 1998AJ....115.2359K)
20- 25 F6.3 mag Kmag 2MASS K-band magnitude
27- 28 I2 h RAh Hour of Right Ascension (J2000)
30- 31 I2 min RAm Minute of Right Ascension (J2000)
33- 37 F5.2 s RAs Second of Right Ascension (J2000)
38 A1 --- DE- Sign of the Declination (J2000)
39- 40 I2 deg DEd Degree of Declination (J2000)
42- 43 I2 arcmin DEm Arcminute of Declination (J2000)
45- 49 F5.2 arcsec DEs Arcsecond of Declination (J2000)
51- 54 I4 K Teffph Photometric effective temperature from (V-I) (1)
56- 59 I4 K Teffs Spectroscopic effective temperature (2)
61- 63 F3.1 [cm/s2] logg Surface gravity (1) (2)
65- 68 F4.2 km/s Vt Microturbulence velocity (2)
70- 74 F5.2 [-] [Fe/H] Metallicity (2)
76- 81 F6.1 km/s RV Radial velocity
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Note (1): Calculated assuming a metallicity of [Fe/H]=-2 dex, mass of
0.8 M☉ and distance of 68 kpc.
Note (2): Values found by iteration of the best atmospheric models used to
calculate the spectroscopic abundances (see the text for details).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- El Element
7- 13 F7.2 0.1nm lambda Wavelength of the absorption line λ
(Å)
15- 18 F4.2 eV EP Excitation energy of the lower energy level
20- 25 F6.3 --- loggf Oscilator strength
27- 31 F5.1 0.1pm EW-UMI396 ? Equivalent width of the line measured for
the star UMI396 (mÅ)
33- 37 F5.1 0.1pm EW-UMI718 ? Equivalent width of the line measured for
the star UMI718 (mÅ)
39- 43 F5.1 0.1pm EW-UMI446 ? Equivalent width of the line measured for
the star UMI446 (mÅ)
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 23-Jan-2018