- ID:
- ivo://CDS.VizieR/J/ApJ/705/328
- Title:
- Abundance measurements in Sculptor dSph
- Short Name:
- J/ApJ/705/328
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present measurements of Fe, Mg, Si, Ca, and Ti abundances for 388 radial velocity member stars in the Sculptor dwarf spheroidal galaxy (dSph), a satellite of the Milky Way (MW). This is the largest sample of individual {alpha} element (Mg, Si, Ca, and Ti) abundance measurements in any single dSph. The measurements are made from Keck/Deep Imaging Multi-Object Spectrometer medium-resolution spectra (6400-9000{AA}, R~6500). Based on comparisons to published high-resolution (R>~20000) spectroscopic measurements, our measurements have uncertainties of {alpha}[Fe/H]=0.14 and {alpha}[{alpha}/Fe]=0.13. We have discovered one star with [Fe/H]=-3.80+/-0.28, which is the most metal-poor star known anywhere except the MW halo, but high-resolution spectroscopy is needed to measure this star's detailed abundances.
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- ID:
- ivo://CDS.VizieR/J/ApJ/511/639
- Title:
- Abundances in blue compact galaxies
- Short Name:
- J/ApJ/511/639
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-quality ground-based spectroscopic observations of 54 supergiant H II regions in 50 low-metallicity blue compact galaxies with oxygen abundances 12+Log[O/H] between 7.1 and 8.3. We use the data to determine abundances for the elements N, O, Ne, S, Ar, and Fe. We also analyze Hubble Space Telescope (HST) Faint Object Spectrograph archival spectra of 10 supergiant H II regions to derive C and Si abundances in a subsample of seven blue compact galaxies. The main result of the present study is that none of the heavy element-to-oxygen abundance ratios studied here (C/O, N/O, Ne/O, Si/O, S/O, Ar/O, Fe/O) depend on oxygen abundance for blue compact galaxies with 12+Log[O/H]{<=}7.6 (Z{<=}Z_{solar}/20).
- ID:
- ivo://CDS.VizieR/J/ApJS/191/352
- Title:
- Abundances in stars of Milky Way dwarf satellites
- Short Name:
- J/ApJS/191/352
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of Fe, Mg, Si, Ca, and Ti abundances for 2961 stars in eight dwarf satellite galaxies of the Milky Way (MW): Sculptor, Fornax, Leo I, Sextans, Leo II, Canes Venatici I, Ursa Minor, and Draco. For the purposes of validating our measurements, we also observed 445 red giants in MW globular clusters and 21 field red giants in the MW halo. The measurements are based on Keck/DEIMOS medium-resolution spectroscopy (MRS) combined with spectral synthesis. We estimate uncertainties in [Fe/H] by quantifying the dispersion of [Fe/H] measurements in a sample of stars in monometallic globular clusters (GCs). We estimate uncertainties in Mg, Si, Ca, and Ti abundances by comparing to high-resolution spectroscopic abundances of the same stars. For this purpose, a sample of 132 stars with published high-resolution spectroscopy in GCs, the MW halo field, and dwarf galaxies has been observed with MRS. The standard deviations of the differences in [Fe/H] and <[{alpha}/Fe]> (the average of [Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe]) between the two samples is 0.15 and 0.16, respectively.
- ID:
- ivo://CDS.VizieR/J/AZh/79/867
- Title:
- Abundances of HII regions in blue galaxies
- Short Name:
- J/AZh/79/867
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New expression for the ionization correction factors (ICF) are used to find the nebular-gas compositions in HII regions in blue compact dwarf galaxies (BCD). The abundances of He, N, O, Ne, S, and Ar in 41 HII regions are determined.
- ID:
- ivo://CDS.VizieR/J/ApJ/817/41
- Title:
- Abundances of 4 metal-poor red giants in BooII
- Short Name:
- J/ApJ/817/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution Magellan/MIKE spectra of the four brightest confirmed red giant stars in the ultra-faint dwarf galaxy Bootes II (Boo II). These stars all inhabit the metal-poor tail of the BooII metallicity distribution function. The chemical abundance pattern of all detectable elements in these stars is consistent with that of the Galactic halo. However, all four stars have undetectable amounts of neutron-capture elements Sr and Ba, with upper limits comparable to the lowest ever detected in the halo or in other dwarf galaxies. One star exhibits significant radial velocity variations over time, suggesting it to be in a binary system. Its variable velocity has likely increased past determinations of the Boo II velocity dispersion. Our four stars span a limited metallicity range, but their enhanced {alpha}-abundances and low neutron-capture abundances are consistent with the interpretation that Boo II has been enriched by very few generations of stars. The chemical abundance pattern in Boo II confirms the emerging trend that the faintest dwarf galaxies have neutron-capture abundances distinct from the halo, suggesting the dominant source of neutron-capture elements in halo stars may be different than in ultra-faint dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/855/83
- Title:
- Abundances of very metal-poor stars in Sagittarius
- Short Name:
- J/ApJ/855/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Sagittarius (Sgr) is a massive disrupted dwarf spheroidal galaxy in the Milky Way halo that has undergone several stripping events. Previous chemical studies were restricted mainly to a few, metal-rich ([Fe/H]>~-1) stars that suggested a top-light initial mass function (IMF). Here we present the first high-resolution, very metal-poor ([Fe/H]=-1 to -3) sample of 13 giant stars in the main body of Sgr. We derive abundances of 13 elements, namely C, Ca, Co, Fe, Sr, Ba, La, Ce, Nd, Eu, Dy, Pb, and Th, that challenge the interpretation based on previous studies. Our abundances from Sgr mimic those of the metal-poor halo, and our most metal-poor star ([Fe/H]~-3) indicates a pure r-process pollution. Abundances of Sr, Pb, and Th are presented for the first time in Sgr, allowing for age determination using nuclear cosmochronology. We calculate ages of 9+/-2.5Gyr. Most of the sample stars have been enriched by a range of asymptotic giant branch (AGB) stars with masses between 1.3 and 5M_{sun}_. SgrJ190651.47-320147.23 shows a large overabundance of Pb (2.05dex) and a peculiar abundance pattern best fit by a 3M_{sun}_ AGB star. Based on star-to-star scatter and observed abundance patterns, a mixture of low- and high-mass AGB stars and supernovae (15-25M_{sun}_) is necessary to explain these patterns. The high level (0.29+/-0.05dex) of Ca indicates that massive supernovae must have existed and polluted the early ISM of Sgr before it lost its gas. This result is in contrast with a top-light IMF with no massive stars polluting Sgr.
- ID:
- ivo://CDS.VizieR/J/ApJ/723/1632
- Title:
- Abundance spreads in Bootes I and Segue 1
- Short Name:
- J/ApJ/723/1632
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an AAOmega spectroscopic study of red giants in the ultra-faint dwarf galaxy Bootes I (M_V_~-6) and the Segue 1 system (M_V_~-1.5), either an extremely low luminosity dwarf galaxy or an unusually extended globular cluster. Both Bootes I and Segue 1 have significant abundance dispersions in iron and carbon. Bootes I has a mean abundance of [Fe/H]=-2.55+/-0.11 with an [Fe/H] dispersion of {sigma}=0.37+/-0.08, and abundance spreads of {Delta}[Fe/H]=1.7 and {Delta}[C/H]=1.5. Segue 1 has a mean of [Fe/H]=-2.7+/-0.4 with [Fe/H] dispersion of {sigma}=0.7+/-0.3, and abundances spreads of {Delta}[Fe/H]=1.6 and {Delta}[C/H]=1.2. Moreover, Segue 1 has a radial-velocity member at four half-light radii that is extremely metal-poor and carbon-rich, with [Fe/H]=-3.5, and [C/Fe]=+2.3. Modulo an unlikely non-member contamination, the [Fe/H] abundance dispersion confirms Segue 1 as the least-luminous ultra-faint dwarf galaxy known.
- ID:
- ivo://CDS.VizieR/J/A+A/538/A100
- Title:
- Abundances red giants in Carina dSph
- Short Name:
- J/A+A/538/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ages of individual Red Giant Branch stars can range from 1Gyr old to the age of the Universe, and it is believed that the abundances of most chemical elements in their photospheres remain unchanged with time (those that are not affected by the first dredge-up). This means that they trace the interstellar medium in the galaxy at the time the star formed, and hence the chemical enrichment history of the galaxy. Colour-Magnitude Diagram analysis has shown the Carina dwarf spheroidal to have had an unusually episodic star formation history and this is expected to be reflected in the abundances of different chemical elements.
- ID:
- ivo://CDS.VizieR/J/ApJ/750/91
- Title:
- Ages and metallicities of old stellar systems
- Short Name:
- J/ApJ/750/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a statistical analysis of the properties of a large sample of dynamically hot old stellar systems, from globular clusters (GCs) to giant ellipticals, which was performed in order to investigate the origin of ultracompact dwarf galaxies (UCDs). The data were mostly drawn from Forbes et al. (2008, Cat. J/MNRAS/389/1924). We recalculated some of the effective radii, computed mean surface brightnesses and mass-to-light ratios, and estimated ages and metallicities. We completed the sample with GCs of M31. We used a multivariate statistical technique (K-Means clustering), together with a new algorithm (Gap Statistics) for finding the optimum number of homogeneous sub-groups in the sample, using a total of six parameters (absolute magnitude, effective radius, virial mass-to-light ratio, stellar mass-to-light ratio, and metallicity). We found six groups. FK1 and FK5 are composed of high- and low-mass elliptical galaxies, respectively. FK3 and FK6 are composed of high-metallicity and low-metallicity objects, respectively, and both include GCs and UCDs. Two very small groups, FK2 and FK4, are composed of Local Group dwarf spheroidals. Our groups differ in their mean masses and virial mass-to-light ratios. The relations between these two parameters are also different for the various groups. The probability density distributions of metallicity for the four groups of galaxies are similar to those of the GCs and UCDs. The brightest low-metallicity GCs and UCDs tend to follow the mass-metallicity relation like elliptical galaxies. The objects of FK3 are more metal-rich per unit effective luminosity density than high-mass ellipticals.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/128
- Title:
- alpha & Fe abundances in the giant stellar stream
- Short Name:
- J/ApJ/883/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first measurements of [Fe/H] and [{alpha}/Fe] abundances, obtained using spectral synthesis modeling, for red giant branch stars in M31's giant stellar stream (GSS). The spectroscopic observations, obtained at a projected distance of 17kpc from M31's center, yielded 61 stars with [Fe/H] measurements, including 21 stars with [{alpha}/Fe] measurements, from 112 targets identified as M31 stars. The [Fe/H] measurements confirm the expectation from photometric metallicity estimates that stars in this region of M31's halo are relatively metal rich compared to stars in the Milky Way's inner halo: more than half the stars in the field, including those not associated with kinematically identified substructure, have [Fe/H] abundances >-1.0. The stars in this field are {alpha}-enhanced at lower metallicities, while [{alpha}/Fe] decreases with increasing [Fe/H] above metallicities of [Fe/H]>~-0.9. Three kinematical components have been previously identified in this field: the GSS, a second kinematically cold feature of unknown origin, and M31's kinematically hot halo. We compare probabilistic [Fe/H] and [{alpha}/Fe] distribution functions for each of the components. The GSS and the second kinematically cold feature have very similar abundance distributions, while the halo component is more metal poor. Although the current sample sizes are small, a comparison of the abundances of stars in the GSS field with abundances of M31 halo and dSph stars from the literature indicate that the progenitor of the stream was likely more massive, and experienced a higher efficiency of star formation, than M31's existing dSphs or the dEs NGC147 and NGC185.