Here, we delineate a comprehensive abundance analysis of four r-process enhanced metal-poor stars observed with HORuS spectrograph on a 10-m class telescope, GTC. The high signal-to-noise ratio at ...R≈25000 spectral resolution allowed us to detect 16 light and 20 neutron-capture elements along with Th in two stars. Four of our program stars show signatures of mixing in their atmosphere. Through detailed abundance analysis of four r-process enhanced stars together with already identified r-process-rich stars in literature, we probe the production sites of neutron-capture elements. The Zr/Eu ratio as a function of metallicity shows the evidence of multiple channels for the production of r-process. Thorium to first and second r-process peak elements ratios also support the similar non-universality of neutron-capture elements. An increased sample of r-process enhanced stars will enable us understand different formation channels of neutron capture elements. Using the kinematic analysis, we found the clues of accretion for two of our program stars.
We present a study on the detailed chemical abundances of five new relatively bright r-process-enhanced stars that were initially observed as part of the SDSS/MARVELS pre-survey. These stars were ...selected, on the basis of their metallicities and carbon abundances, among a total of 60 stars, for high-resolution spectroscopic follow-up as part of the HESP-GOMPA survey (Hanle Echelle SPectrograph-Galactic survey Of Metal Poor stArs). Here we discuss the three new r-I and two new r-II stars found in this survey. We have carried out a detailed abundance analysis for each of these stars, at a resolving power of R ∼ 30,000, and we compare our results to the existing literature. We could measure three of the first r-process-peak elements (Sr, Y, and Zr) in all five stars, while Ba, Ce, Nd, Sm, Eu, and Dy could be detected among the second r-process-peak elements. Thorium could also be detected in one of the targets, which is found to be an actinide-boost star. We have carried out a comparative study among the subpopulations of the r-process-enhanced stars and other stars of the Milky Way halo population to constrain the origin of this class of objects. These bright r-process-enhanced stars provide an excellent opportunity to study the nucleosynthesis history of this population in great detail, and shed light on their chemical-enrichment histories.
Abstract
We present a study on the detailed elemental abundances of newly identified, bright, very metal-poor stars with the detection of lithium, initially observed as part of the SDSS/MARVELS ...pre-survey. These stars were selected for high-resolution spectroscopic follow-up as part of the HESP-GOMPA survey. In this work, we discuss the Li abundances detected for several stars in the survey, which include main-sequence stars, subgiants, and red giants. Different classes of stars are found to exhibit very similar distributions of Li, which points toward a common origin. We derive a scaling relation for the depletion of Li as a function of temperature for giants and main-sequence stars; the majority of the samples from the literature were found to fall within 1
σ
(0.19 and 0.12 dex K
−1
for giants and dwarfs, respectively) of this relationship. We also report the existence of a slope of the Li abundance as a function of distance from the Galactic plane, indicating mixed stellar populations. Most Li-rich stars are found to be in or close to the Galactic plane. Along with Li, we have derived detailed abundances for C, odd-
Z
,
α
-, Fe-peak, and neutron-capture elements for each star. We have also used astrometric parameters from Gaia-EDR3 to complement our study, and derived kinematics to differentiate between the motions of the stars—those formed in situ and those accreted. The stellar population of the Spite plateau, including additional stars from the literature, is found to have significant contributions from stars formed in situ and through accretion. The orbits for the program stars have also been derived and studied for a period of 5 Gyr backwards in time.
We describe a method for the determination of stellar C/Fe abundance ratios using low-resolution (R = 2000) stellar spectra from the Sloan Digital Sky Survey (SDSS) and its Galactic sub-survey, the ...Sloan Extension for Galactic Understanding and Exploration (SEGUE). By means of a star-by-star comparison with a set of SDSS/SEGUE spectra with available estimates of C/Fe based on published high-resolution analyses, we demonstrate that we can measure C/Fe from SDSS/SEGUE spectra with S/N > or =, slanted 15 A super(-1) to a precision better than 0.35 dex for stars with atmospheric parameters in the range T sub(eff) = 4400, 6700 K, log g = 1.0, 5.0, Fe/H = -4.0, +0.5, and C/Fe = -0.25, +3.5. We find that the differential frequency slowly rises from almost zero to about 14% at Fe/H ~ -2.4, followed by a sudden increase, by about a factor of three, to 39% from Fe/H ~ -2.4 to Fe/H ~ -3.7.
ABSTRACT
Comet 2I/Borisov is the first true interstellar comet discovered. Here, we present results from observational programs at two Indian observatories, 2 m Himalayan Chandra Telescope at the ...Indian Astronomical Observatory, Hanle (HCT) and 1.2 m telescope at the Mount Abu Infrared Observatory (MIRO). Two epochs of imaging and spectroscopy were carried out at the HCT and three epochs of imaging at MIRO. We found CN to be the dominant molecular emission on both epochs, 2019 November 30 and December 22, at distances of rH = 2.013 and 2.031 au, respectively. The comet was inferred to be relatively depleted in Carbon bearing molecules on the basis of low C2 and C3 abundances. We find the production rate ratio, Q(C2)/Q(CN) = 0.54 ± 0.18, pre-perihelion and Q(C2)/Q(CN) = 0.34 ± 0.12 post-perihelion. This classifies the comet as being moderately depleted in carbon chain molecules. Using the results from spectroscopic observations, we believe the comet to have a chemically heterogeneous surface having variation in abundance of carbon chain molecules. From imaging observations, we infer a dust-to-gas ratio similar to carbon chain depleted comets of the Solar system. We also compute the nucleus size to be in the range 0.18 km ≤ r ≤ 3.1 km. Our observations show that 2I/Borisov’s behaviour is analogous to that of the Solar system comets.
Abstract
The correlation between host star iron abundance and the exoplanet occurrence rate is well established and arrived at in several studies. Similar correlations may be present for the most ...abundant elements, such as carbon and oxygen, which also control the dust chemistry of the protoplanetary disk. In this paper, using a large number of stars in the Kepler field observed by the LAMOST survey, it has been possible to estimate the planet occurrence rate with respect to the host star carbon abundance. Carbon abundances are derived using synthetic spectra fit of the
CH
-
G
-band region in the LAMOST spectra. The carbon abundance trend with metallicity is consistent with the previous studies and follows the Galactic chemical evolution (GCE). Similar to Fe/H, we find that the C/H values are higher among giant-planet hosts. The trend between C/Fe and Fe/H in planet hosts and single stars is similar; however, there is a preference for giant planets around host stars with a subsolar C/Fe ratio and higher Fe/H. Higher metallicity and subsolar C/Fe values are found among younger stars as a result of GCE. Hence, based on the current sample, it is difficult to interpret the results as a consequence of GCE or due to planet formation.
Recent studies of the time-resolved Milky Way formation using asteroseismology have shown that thick disk stars could be very old (0.8 Gyr after the Big Bang, even older than the inner halo). ...Additionally, thick disk stars are expected to have formed from a mixed gas and offer a better site to study the chemical enrichment history. Here, we present abundance trends for about 65 metal-poor stars (•3.1 < Fe/H < •1.8) that are kinematically separated into thick disk, and halo, observed with the HESP spectrograph installed at HCT telescope. The sample includes 40 newly identified stars combined with 25 stars from an earlier HESP-GOMPA survey and a compilation from literature. Generally, thick disk stars show less scatter than the halo stars. The abundance trend in Mg/Fe as a function of metallicity remains flat for thick disk stars, indicating similar enrichment history and well-mixed ISM with only massive star contribution, whereas the halo stars show a large scatter and a declining trend in Mg/Fe as a function of metallicity. The Eu/Mg trend show a mildly increasing trend indicating some delay in the production of Eu as compared to Mg, in both halo and the thick disk stars. The scatter in the abundance trend is larger in the halo as compared to thick disk stars, indicating that the halo is formed from accretion of multiple stellar systems.
Carbon-enhanced metal-poor (CEMP) stars in the halo components of the Milky Way are explored, based on accurate determinations of the carbon-to-iron (C/Fe) abundance ratios and kinematic quantities ...for over 30,000 calibration stars from the Sloan Digital Sky Survey. Using our present criterion that low-metallicity stars exhibiting C/Fe ratios ("carbonicity") in excess of C/Fe = +0.7 are considered CEMP stars, the global frequency of CEMP stars in the halo system for Fe/H < -1.5 is 8%, for Fe/H < -2.0 it is 12%, and for Fe/H < -2.5 it is 20%. Based on a statistical separation of the halo components in velocity space, we find evidence for a significant contrast in the frequency of CEMP stars between the inner- and outer-halo components -- the outer halo possesses roughly twice the fraction of CEMP stars as the inner halo.
Abstract
We report the discovery of TOI-2180 b, a 2.8
M
J
giant planet orbiting a slightly evolved G5 host star. This planet transited only once in Cycle 2 of the primary Transiting Exoplanet Survey ...Satellite (TESS) mission. Citizen scientists identified the 24 hr single-transit event shortly after the data were released, allowing a Doppler monitoring campaign with the Automated Planet Finder telescope at Lick Observatory to begin promptly. The radial velocity observations refined the orbital period of TOI-2180 b to be 260.8 ± 0.6 days, revealed an orbital eccentricity of 0.368 ± 0.007, and discovered long-term acceleration from a more distant massive companion. We conducted ground-based photometry from 14 sites spread around the globe in an attempt to detect another transit. Although we did not make a clear transit detection, the nondetections improved the precision of the orbital period. We predict that TESS will likely detect another transit of TOI-2180 b in Sector 48 of its extended mission. We use giant planet structure models to retrieve the bulk heavy-element content of TOI-2180 b. When considered alongside other giant planets with orbital periods over 100 days, we find tentative evidence that the correlation between planet mass and metal enrichment relative to stellar is dependent on orbital properties. Single-transit discoveries like TOI-2180 b highlight the exciting potential of the TESS mission to find planets with long orbital periods and low irradiation fluxes despite the selection biases associated with the transit method.
The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, and this information can be used to tightly constrain models of ...galaxy formation and evolution. Although the halo was once considered a single component, evidence for its dichotomy has slowly emerged in recent years from inspection of small samples of halo objects. Here we show that the halo is indeed clearly divisible into two broadly overlapping structural components--an inner and an outer halo--that exhibit different spatial density profiles, stellar orbits and stellar metallicities (abundances of elements heavier than helium). The inner halo has a modest net prograde rotation, whereas the outer halo exhibits a net retrograde rotation and a peak metallicity one-third that of the inner halo. These properties indicate that the individual halo components probably formed in fundamentally different ways, through successive dissipational (inner) and dissipationless (outer) mergers and tidal disruption of proto-Galactic clumps.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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