- ID:
- ivo://CDS.VizieR/J/ApJ/711/350
- Title:
- Metal-poor giant Boo-1137 abundances
- Short Name:
- J/ApJ/711/350
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution (R~40000), high-signal-to-noise ratio (20-90) spectra of an extremely metal-poor giant star Boo-1137 in the "ultra-faint" dwarf spheroidal galaxy (dSph) Bootes I, absolute magnitude M_V_~-6.3. We derive an iron abundance of [Fe/H]=-3.7, making this the most metal-poor star as yet identified in an ultra-faint dSph. Our derived effective temperature and gravity are consistent with its identification as a red giant in Bootes I. Abundances for a further 15 elements have also been determined. Comparison of the relative abundances, [X/Fe], with those of the extremely metal-poor red giants of the Galactic halo shows that Boo-1137 is "normal" with respect to C and N, the odd-Z elements Na and Al, the iron-peak elements, and the neutron-capture elements Sr and Ba, in comparison with the bulk of the Milky Way halo population having [Fe/H]<~-3.0. The {alpha}-elements Mg, Si, Ca, and Ti are all higher by {Delta}[X/Fe]~0.2 than the average halo values. Monte Carlo analysis indicates that {Delta}[{alpha}/Fe] values this large are expected with a probability ~0.02. The elemental abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution, consistent with the wide internal spread in iron abundances we previously reported.
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- ID:
- ivo://CDS.VizieR/J/ApJ/874/148
- Title:
- Metal-poor star RAVE J093730.5-062655 abundances
- Short Name:
- J/ApJ/874/148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new moderately r-process-enhanced metal-poor star, RAVEJ093730.5-062655, has been identified in the Milky Way halo as part of an ongoing survey by the R-Process Alliance. The temperature and surface gravity indicate that J0937-0626 is likely a horizontal branch star. At [Fe/H]=-1.86, J0937-0626 is found to have subsolar [X/Fe] ratios for nearly every light, {alpha}, and Fe-peak element. The low [{alpha}/Fe] ratios can be explained by an ~0.6dex excess of Fe; J0937-0626 is therefore similar to the subclass of "iron-enhanced" metal-poor stars. A comparison with Milky Way field stars at [Fe/H]=-2.5 suggests that J0937-0626 was enriched in material from an event, possibly a Type Ia supernova, that created a significant amount of Cr, Mn, Fe, and Ni and smaller amounts of Ca, Sc, Ti, and Zn. The r-process enhancement of J0937-0626 is likely due to a separate event, which suggests that its birth environment was highly enriched in r-process elements. The kinematics of J0937-0626, based on Gaia DR2 data, indicate a retrograde orbit in the Milky Way halo; J0937-0626 was therefore likely accreted from a dwarf galaxy that had significant r-process enrichment.
- ID:
- ivo://CDS.VizieR/J/ApJ/781/40
- Title:
- Metal-poor stars from HES survey. II. Spectroscopy
- Short Name:
- J/ApJ/781/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the discovery of seven low-metallicity stars selected from the Hamburg/ESO Survey, six of which are extremely metal-poor (EMP, [Fe/H]{<=}-3.0), with four having [Fe/H]{<=}-3.5. Chemical abundances or upper limits are derived for these stars based on high-resolution (R~35000) Magellan/MIKE spectroscopy, and are in general agreement with those of other very and extremely metal-poor stars reported in the literature. Accurate metallicities and abundance patterns for stars in this metallicity range are of particular importance for studies of the shape of the metallicity distribution function of the Milky Way's halo system, in particular for probing the nature of its low-metallicity tail. In addition, taking into account suggested evolutionary mixing effects, we find that six of the program stars (with [Fe/H]{<=}-3.35) possess atmospheres that were likely originally enriched in carbon, relative to iron, during their main-sequence phases. These stars do not exhibit overabundances of their s-process elements, and hence may be, within the error bars, additional examples of the so-called CEMP-no class of objects.
- ID:
- ivo://CDS.VizieR/J/AJ/154/52
- Title:
- Metal-poor stars from SDSS/SEGUE. I Unevolved stars
- Short Name:
- J/AJ/154/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present elemental abundances for eight unevolved extremely metal-poor (EMP) stars with T_eff_>5500K, among which seven have [Fe/H]{<}-3.5. The sample is selected from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE) and our previous high-resolution spectroscopic follow-up with the Subaru Telescope. Several methods to derive stellar parameters are compared, and no significant offset in the derived parameters is found in most cases. From an abundance analysis relative to the standard EMP star G64-12, an average Li abundance for stars with [Fe/H]<-3.5 is A(Li)=1.90, with a standard deviation of {sigma}=0.10dex. This result confirms that lower Li abundances are found at lower metallicity, as suggested by previous studies, and demonstrates that the star-to-star scatter is small. The small observed scatter could be a strong constraint on Li-depletion mechanisms proposed for explaining the low Li abundance at lower metallicity. Our analysis for other elements obtained the following results: (i) a statistically significant scatter in [X/Fe] for Na, Mg, Cr, Ti, Sr, and Ba, and an apparent bimodality in [Na/Fe] with a separation of ~0.8dex, (ii) an absence of a sharp drop in the metallicity distribution, and (iii) the existence of a CEMP-s star at [Fe/H]{simeq}-3.6 and possibly at [Fe/H]{simeq}-4.0, which may provide a constraint on the mixing efficiency of unevolved stars during their main-sequence phase.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A124
- Title:
- Metal-poor stars towards the Galactic bulge
- Short Name:
- J/A+A/587/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the south- ern edge of the Galactic bulge, at (l, b)~(0{deg}, -11{deg}). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H]=-2.52dex, and another target is a moderately metal-poor ([Fe/H]=-1.53dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe]=1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning -2.0 to -2.6dex, i.e., enhanced {alpha}-elements and solar Fe-peak and neutron-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with simulations of the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their highly uncertain proper motions prohibit a clear kinematic separation, the stars' chemical abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge.
- ID:
- ivo://CDS.VizieR/J/ApJ/875/89
- Title:
- Metal-poor stars with APF. I. LAMOST CEMP stars
- Short Name:
- J/ApJ/875/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the discovery of five carbon-enhanced metal-poor (CEMP) stars in the metallicity range of -3.3<[Fe/H]{<}-2.4. These stars were selected from the LAMOST DR3 low-resolution (R~2000) spectroscopic database as metal-poor candidates and followed up with high-resolution spectroscopy (R~110000) with the Lick/APF. Stellar parameters and individual abundances for 25 chemical elements (from Li to Eu) are presented for the first time. These stars exhibit chemical abundance patterns that are similar to those reported in other literature studies of very and extremely metal-poor stars. One of our targets, J2114-0616, shows high enhancement in carbon ([C/Fe]=1.37), nitrogen ([N/Fe]=1.88), barium ([Ba/Fe]=1.00), and europium ([Eu/Fe]=0.84). Such chemical abundance pattern suggests that J2114-0616 can be classified as CEMP-r/s star. In addition, the star J1054+0528 can be classified as a CEMP-rI star, with [Eu/Fe]=0.44 and [Ba/Fe]=-0.52. The other stars in our sample show no enhancements in neutron-capture elements and can be classified as CEMP-no stars. We also performed a kinematic and dynamical analysis of the sample stars based on Gaia DR2 data. The kinematic parameters, orbits, and binding energy of these stars show that J2114-0616 is member of the outer-halo population, while the remaining stars belong to the inner-halo population but with an accreted origin. Collectively, these results add important constraints on the origin and evolution of CEMP stars as well as on their possible formation scenarios.
- ID:
- ivo://CDS.VizieR/J/ApJ/882/27
- Title:
- Metal-poor stars with APF obs. II. MW halo stars
- Short Name:
- J/ApJ/882/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we study the chemical compositions and kinematic properties of six metal-poor stars with [Fe/H]{<}-2.5 in the Galactic halo. From high-resolution (R~110000) spectroscopic observations obtained with the Lick/Automated Planet Finder, we determined individual abundances for up to 23 elements, to quantitatively evaluate our sample. We identify two carbon-enhanced metal-poor stars (J1630+0953 and J2216+0246) without enhancement in neutron-capture elements (CEMP-no stars), while the rest of our sample stars are carbon-intermediate. By comparing the light-element abundances of the CEMP stars with predicted yields from nonrotating zero-metallicity massive-star models, we find that the possible progenitors of J1630+0953 and J2216+0246 could be in the 13-25M_{sun}_ mass range, with explosion energies (0.3-1.8)x10^51^erg. In addition, the detectable abundance ratios of light and heavy elements suggest that our sample stars are likely formed from a well-mixed gas cloud, which is consistent with previous studies. We also present a kinematic analysis, which suggests that most of our program stars likely belong to the inner-halo population, with orbits passing as close as ~2.9kpc from the Galactic center. We discuss the implications of these results on the critical constraints on the origin and evolution of CEMP stars, as well as the nature of the Population III progenitors of the lowest-metallicity stars in our Galaxy.
- ID:
- ivo://CDS.VizieR/J/AJ/106/1839
- Title:
- Metal-rich halo A stars
- Short Name:
- J/AJ/106/1839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of spectrophotometry of the Ca II K and Balmer lines and radial velocity measurements for stars earlier than type F0, with 10<V<15.5 in fields at (l;b)=(90deg, 270deg; -45deg) are reported. Slit spectroscopy of 320 stars shows that in this magnitude range there are ~80 stars with [Fe/H]>-0.5. The metal-rich population has a vertical scale height of ~600pc and a space density at the Sun equal to 1/225 of the young thin disk A star population. The metal-rich A stars have V_rot_=210+/-60km/s with decreasing angular momentum as a function of distance from the Galactic plane. The line-of-sight velocity dispersion is 40+/-3km/s indicating an anomalous relation between structure and kinematics. There is strong evidence that these stars are identical in properties to the metal-rich extended populations found by Perry [1969AJ.....74..139P] at the NGP and Rodgers [1971ApJ...165..581R] at the SGP.
- ID:
- ivo://CDS.VizieR/J/AJ/158/239
- Title:
- Metal-rich host stars abundances & equivalent widths
- Short Name:
- J/AJ/158/239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relationship between the compositions of giant planets and their host stars is of fundamental interest in understanding planet formation. The solar system giant planets are enhanced above solar composition in metals, both in their visible atmospheres and bulk compositions. A key question is whether the metal enrichment of giant exoplanets is correlated with that of their host stars. Thorngren et al. (2016, J/ApJ/831/64) showed that in cool (T_eq_<1000 K) giant exoplanets, the total heavy-element mass increases with total M_p_ and the heavy-element enrichment relative to the parent star decreases with total M_p_. In their work, the host star metallicity was derived from literature [Fe/H] measurements. Here we conduct a more detailed and uniform study to determine whether different host star metals (C, O, Mg, Si, Fe, and Ni) correlate with the bulk metallicity of their planets, using correlation tests and Bayesian linear fits. We present new host star abundances of 19 cool giant planet systems, and combine these with existing host star data for a total of 22 cool giant planet systems (24 planets). Surprisingly, we find no clear correlation between stellar metallicity and planetary residual metallicity (the relative amount of metal versus that expected from the planet mass alone), which is in conflict with common predictions from formation models. We also find a potential correlation between residual planet metals and stellar volatile-to-refractory element ratios. These results provide intriguing new relationships between giant planet and host star compositions for future modeling studies of planet formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/37
- Title:
- Metals in SDSS QSOs. I. 1.5<z<4.5 CIV absorbers
- Short Name:
- J/ApJ/763/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have vastly increased the CIV statistics at intermediate redshift by surveying the thousands of quasars in the Sloan Digital Sky Survey (SDSS) Data-Release 7. We visually verified over 16000 CIV systems with 1.46<z<4.55 - a sample size that renders Poisson error negligible. Detailed Monte Carlo simulations show that we are approximately 50% complete down to rest equivalent widths W_r_{approx}0.6{AA}. We analyzed the sample as a whole and in 10 small redshift bins with approximately 1500 doublets each. The equivalent width frequency distributions f(W_r_) were well modeled by an exponential, with little evolution in shape. In contrast with previous studies that modeled the frequency distribution as a single power law, the fitted exponential gives a finite mass density for the CIV ions. The comoving line density dN_CIV_/dX evolved smoothly with redshift, increasing by a factor of 2.37+/-0.09 from z=4.55-1.96, then plateauing at dN_CIV_/dX~0.34 for z=1.96-1.46. Comparing our SDSS sample with z<1 (ultraviolet) and z>5 (infrared) surveys, we see an approximately 10-fold increase in dN_CIV_/dX over z{approx}6->0, for W_r_>=0.6{AA}. This suggests a monotonic and significant increase in the enrichment of gas outside galaxies over the 12Gyr lifetime of the universe.
