Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA New CEMP-s RR Lyrae Star
100
0
0.0
(
0
)
Authors
T. D. Kinman
Ask ChatGPT about the research
No Arabic abstract
We show that SDSS J170733.93+585059.7 (hereafter SDSS J1707+58), previously identified by Aoki and collaborators as a carbon-enhanced metal-poor star (with s-process-element enhancements; CEMP-s), on the assumption that it is a main-sequence turn-off star, is the RR Lyrae star VIII-14 identified by the Lick Astrograph Survey. Revised abundances for SDSS J1707+58 are [Fe/H] = -2.92, [C/Fe] = +2.79, and [Ba/Fe] = +2.83. It is thus one of the most metal-poor RR Lyrae stars known, and has more extreme [C/Fe] and [Ba/Fe] than the only other RR Lyrae star known to have a CEMP-s spectrum (TY Gru). Both stars are Oosterhoff II stars with prograde kinematics, in contrast to stars with [C/Fe] < +0.7, such as KP Cyg and UY CrB, which are disk stars. Twelve other RR Lyrae stars with [C/Fe] >= +0.7 are presented as CEMP candidates for further study.
rate research
Read More
We apply the GC3 stream-finding method to RR Lyrae stars (RRLS) in the Catalina survey. We find two RRLS stream candidates at $>4sigma$ confidence and another 12 at $>3.5sigma$ confidence over the Galactocentric distance range $4 < D/{rm kpc} < 26$. Of these, only two are associated with known globular clusters (NGC 1261 and Arp2). The remainder are candidate `orphan streams, consistent with the idea that globular cluster streams are most visible close to dissolution. Our detections are likely a lower bound on the total number of dissolving globulars in the inner galaxy, since many globulars have few RRLS while only the brightest streams are visible over the Galactic RRLS background, particularly given the current lack of kinematical information. We make all of our candidate streams publicly available and provide a new GALSTREAMS Python library for the footprints of all known streams and overdensities in the Milky Way.
The serendipitous discovery by Preston and colleagues of the neutron-capture-enhanced RR Lyrae variable star TY Gru (a.k.a. CS 22881-071 in the HK survey of very metal-poor halo stars) has resulted in a growing set of initiatives on the chemical compositions of RR Lyrae stars and their application to broader topics in Galactic halo structure. Here we summarize the main aspects of our work on TY Gru, including a new discussion of our search for possible orbital motion of this star around a putative unseen companion. Then we describe a few of the results of a newly-completed intensive spectroscopic investigation of 10 additional field RR Lyr stars. We finish by outlining current projects that seek to contrast the atmospheres and chemical compositions of RRc stars with those of the RRab stars, and that employ a much larger RRab sample in a chemo-dynamical study of Galactic halo RR Lyr.
Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time effect in so-called observed minus calculated ($O-C$) diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III data revealed an initial sample of 29 candidates. We used the recently released OGLE-IV data to extend the baselines up to 17 years, leading to a final sample of 12 firm binary candidates. We provide $O-C$ diagrams and binary parameters for this final sample, and also discuss the properties of 8 additional candidate binaries whose parameters cannot be firmly determined at present. We also estimate that $gtrsim 4$ per cent of the RRL reside in binary systems.
We use deep multi-epoch near-IR images of the VISTA Variables in the Via Lactea (VVV) Survey to search for RR Lyrae stars towards the Southern Galactic plane. Here we report the discovery of a group of RR Lyrae stars close together in VVV tile d025. Inspection of the VVV images and PSF photometry reveals that most of these stars are likely to belong to a globular cluster, that matches the position of the previously known star cluster FSR,1716. The stellar density map of the field yields a $>100$ sigma detection for this candidate globular cluster, that is centered at equatorial coordinates $RA_{J2000}=$16:10:30.0, $DEC_{J2000}=-$53:44:56; and galactic coordinates $l=$329.77812, $b=-$1.59227. The color-magnitude diagram of this object reveals a well populated red giant branch, with a prominent red clump at $K_s=13.35 pm 0.05$, and $J-K_s=1.30 pm 0.05$. We present the cluster RR Lyrae positions, magnitudes, colors, periods and amplitudes. The presence of RR Lyrae indicates an old globular cluster, with age $>10$ Gyr. We classify this object as an Oosterhoff type I globular cluster, based on the mean period of its RR Lyrae type ab, $<P>=0.540$ days, and argue that this is a relatively metal-poor cluster with $[Fe/H] = -1.5 pm 0.4$ dex. The mean extinction and reddening for this cluster are $A_{K_s}=0.38 pm 0.02$, and $E(J-K_s)=0.72 pm 0.02$ mag, respectively, as measured from the RR Lyrae colors and the near-IR color-magnitude diagram. We also measure the cluster distance using the RR Lyrae type ab stars. The cluster mean distance modulus is $(m-M)_0 = 14.38 pm 0.03$ mag, implying a distance $D = 7.5 pm 0.2$ kpc, and a Galactocentric distance $R_G=4.3$ kpc.
We present the results of a deep, wide-area variability survey in the Southern hemisphere, the first of its kind. As part of the Catalina Sky Surveys, the Siding Spring Survey (SSS) has covered $14,800$ square degrees in the declination range of $-75^{circ}leqdeltaleq-15^{circ}$. To mine the enormous SSS dataset efficiently we have developed two algorithms: Automatic Period Selection (APS) and Automatic Fourier Decomposition (AFD), which aim to sharpen the period estimation and produce robust lightcurve models. Armed with the APS and AFD outputs we classify $10,540$ ab-type RR Lyrae (RRab) stars ($sim$90% of which are new) across the Southern sky. As well as the positional information we supply photometric metallicities, and unreddened distances. For the RRab stars in the halo, a study of the photometric metallicity distribution reveals a nearly Gaussian shape with a mean metallicity of ${rm [Fe/H]}=-1.4$ dex and a dispersion of $0.3$ dex. A spatial study of the RRab metallicities shows no significant radial gradient in the first $sim7$ kpc from the Galaxy center. However, further out, a small negative gradient is clearly present. This is complemented by a very obvious correlation of the mean RR Lyrae metallicity with distance above the Galactic plane, $z$. We have also carried out an initial substructure search using the discovered RRab, and present the properties of the candidates with significance greater than $2 sigma$. Most prominent among these is a southern extension of the Sagittarius dwarf galaxys stream system, reaching down to declinations $sim -40deg$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
