Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Hyades open cluster is chemically inhomogeneous
59
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present a high-precision differential abundance analysis of 16 solar-type stars in the Hyades open cluster based on high resolution, high signal-to-noise ratio (S/N ~ 350 - 400) spectra obtained from the McDonald 2.7m telescope. We derived stellar parameters and differential chemical abundances for 19 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ba) with uncertainties as low as ~ 0.01 - 0.02 dex. Our main results include: (1) there is no clear chemical signature of planet formation detected among the sample stars, i.e., no correlations in abundances versus condensation temperature; (2) the observed abundance dispersions are a factor of ~ 1.5 - 2 larger than the average measurement errors for most elements; (3) there are positive correlations, of high statistical significance, between the abundances of at least 90% of pairs of elements. We demonstrate that none of these findings can be explained by errors due to the stellar parameters. Our results reveal that the Hyades is chemically inhomogeneous at the 0.02 dex level. Possible explanations for the abundance variations include (1) inhomogeneous chemical evolution in the proto-cluster environment, (2) supernova ejection in the proto-cluster cloud, and (3) pollution of metal-poor gas before complete mixing of the proto-cluster cloud. Our results provide significant new constraints on the chemical composition of open clusters and a challenge to the current view of Galactic archeology.
rate research
Read More
We present the first high-angular resolution survey for multiple systems among very low-mass stars and brown dwarfs in the Hyades open cluster. Using the Keck,II adaptive optics system, we observed a complete sample of 16 objects with estimated masses $lesssim$0.1 Msun. We have identified three close binaries with projected separation $lesssim$0.11, or $lesssim$5 AU. A number of wide, mostly faint candidate companions are also detected in our images, most of which are revealed as unrelated background sources based on astrometric and/or photometric considerations. The derived multiplicity frequency, 19+13/-6 % over the 2-350 AU range, and the rarity of systems wider than 10 AU are both consistent with observations of field very low-mass objects. In the limited 3-50 AU separation range, the companion frequency is essentially constant from brown dwarfs to solar-type stars in the Hyades cluster, which is also in line with our current knowledge for field stars. Combining the binaries discovered in this surveys with those already known in the Pleiades cluster reveals that very low-mass binaries in open clusters, as well as in star-forming regions, are skewed toward lower mass ratios ($0.6 lesssim q lesssim 0.8$) than are their field counterparts, a result that cannot be accounted for by selection effects. Although the possibility of severe systematic errors in model-based mass estimates for very low-mass stars cannot be completely excluded, it is unlikely to explain this difference. We speculate that this trend indicates that surveys among very low-mass field stars may have missed a substantial population of intermediate mass ratio systems, implying that these systems are more common and more diverse than previously thought.
We have derived accurate and homogeneous Lithium abundances in 49 main sequence binary systems belonging to the Hyades Open Cluster by using a deconvolution method to determine individual magnitudes and colors for the primary and secondary components of the binary. The input parameters of the model are the observed Li equivalent width, the actual distance to the binary, the integrated apparent magnitude and the integrated colors of the binaries -BV(RI)_K. We show that the general behavior is the same in binaries and in single stars (Li is depleted faster in K stars than in G stars and there is a deep dip for mid-F stars). However, there is a larger scatter in the abundances of binary systems than in single stars. Moreover, in general, binary systems have an overabundance, which is more conspicuous in close binaries. In fact, there is a cut-off period, which can be estimated as P(orb)~9 d. This value is in excellent agreement with the theoretical predition of Zahn (1994).
We report the discovery of the first hot Jupiter in the Hyades open cluster. HD 285507b orbits a V=10.47 K4.5V dwarf ($M_* = 0.734 M_odot$; $R_* = 0.656 R_odot$) in a slightly eccentric ($e = 0.086^{+0.018}_{-0.019}$) orbit with a period of $6.0881^{+0.0019}_{-0.0018}$ days. The induced stellar radial velocity corresponds to a minimum companion mass of $M_{rm p} sin{i} = 0.917 pm 0.033 M_{rm Jup}$. Line bisector spans and stellar activity measures show no correlation with orbital phase, and the radial velocity amplitude is independent of wavelength, supporting the conclusion that the variations are caused by a planetary companion. Follow-up photometry indicates with high confidence that the planet does not transit. HD 285507b joins a small but growing list of planets in open clusters, and its existence lends support to a planet formation scenario in which a high stellar space density does not inhibit giant planet formation and migration. We calculate the circularization timescale for HD 285507b to be larger than the age of the Hyades, which may indicate that this planets non-zero eccentricity is the result of migration via interactions with a third body. We also demonstrate a significant difference between the eccentricity distributions of hot Jupiters that have had time to tidally circularize and those that have not, which we interpret as evidence against Type II migration in the final stages of hot Jupiter formation. Finally, the dependence of the circularization timescale on the planetary tidal quality factor, $Q_{rm p}$, allows us to constrain the average value for hot Jupiters to be $log{Q_{rm p}} = 6.14^{+0.41}_{-0.25}$.
Stellar kinematic groups are kinematical coherent groups of stars that might have a common origin. These groups are dispersed throughout the Galaxy over time by the tidal effects of both Galactic rotation and disc heating, although their chemical content remains unchanged. The aim of chemical tagging is to establish that the abundances of every element in the analysis are homogeneus among the members. We study the case of the Hyades Supercluster to compile a reliable list of members (FGK stars) based on our chemical tagging analysis. For a total of 61 stars from the Hyades Supercluster, stellar atmospheric parameters (Teff, logg, xi, and [Fe/H]) are determined using our code called StePar, which is based on the sensitivity to the stellar atmospheric parameters of the iron EWs measured in the spectra. We derive the chemical abundances of 20 elements and find that their [X/Fe] ratios are consistent with Galactic abundance trends reported in previous studies. The chemical tagging method is applied with a carefully developed differential abundance analysis of each candidate member of the Hyades Supercluster, using a well-known member of the Hyades cluster as a reference (vB 153). We find that only 28 stars (26 dwarfs and 2 giants) are members, i.e. that 46% of our candidates are members based on the differential abundance analysis. This result confirms that the Hyades Supercluster cannot originate solely from the Hyades cluster.
The Hyades open cluster was targeted during Campaign 4 (C4) of the NASA K2 mission, and short-cadence data were collected on a number of cool main-sequence stars. Here, we report results on two F-type stars that show detectable oscillations of a quality that allows asteroseismic analyses to be performed. These are the first ever detections of solar-like oscillations in main-sequence stars in an open cluster.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
