Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFSR 1716: A new Milky Way Globular Cluster confirmed using VVV RR Lyrae stars
124
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
We present a chemo-dynamical study of the Orphan stellar stream using a catalog of RR~Lyrae pulsating variable stars for which photometric, astrometric, and spectroscopic data are available. Employing low-resolution spectra from the Sloan Digital Sky Survey (SDSS), we determined line-of-sight velocities for individual exposures and derived the systemic velocities of the RR~Lyrae stars. In combination with the stars spectroscopic metallicities and textit{Gaia} EDR3 astrometry, we investigated the northern part of the Orphan stream. In our probabilistic approach, we found 20 single mode RR~Lyrae variables likely associated with the Orphan stream based on their positions, proper motions, and distances. The acquired sample permitted us to expand our search to nonvariable stars in the SDSS dataset, utilizing line-of-sight velocities determined by the SDSS. We found 54 additional nonvariable stars linked to the Orphan stream. The metallicity distribution for the identified red giant branch stars and blue horizontal branch stars is, on average, $-2.13pm0.05$ dex and $-1.87pm0.14$ dex, with dispersions of 0.23 and 0.43dex, respectively. The metallicity distribution of the RR~Lyrae variables peaks at $-1.80pm0.06$ dex and a dispersion of 0.25dex. Using the collected stellar sample, we investigated a possible link between the ultra-faint dwarf galaxy Grus II and the Orphan stream. Based on their kinematics, we found that both the stream RR~Lyrae and Grus II are on a prograde orbit with similar orbital properties, although the large uncertainties on the dynamical properties render an unambiguous claim of connection difficult. At the same time, the chemical analysis strongly weakens the connection between both. We argue that Grus II in combination with the Orphan stream would have to exhibit a strong inverse metallicity gradient, which to date has not been detected in any Local Group system.
RR Lyrae stars being distance indicators and tracers of old population serve as excellent probes of the structure, formation, and evolution of our Galaxy. Thousands of them are being discovered in ongoing wide-field surveys. The OGLE project conducts the Galaxy Variability Survey with the aim to detect and analyze variable stars, in particular of RRab type, toward the Galactic bulge and disk, covering a total area of 3000 deg^2. Observations in these directions also allow detecting background halo variables and unique studies of their properties and distribution at distances from the Galactic Center to even 40 kpc. In this contribution, we present the first results on the spatial distribution of the observed RRab stars, their metallicity distribution, the presence of multiple populations, and relations with the old bulge. We also show the most recent results from the analysis of RR Lyrae stars of the Sgr dwarf spheroidal galaxy, including its center, the globular cluster M54.
In order to characterize 22 new globular cluster (GC) candidates in the Galactic bulge, we present their colour-magnitude diagrams (CMDs) and Ks-band luminosity functions (LFs) using the near-infrared VVV database as well as Gaia-DR2 proper motion dataset. CMDs were obtained, on one hand, after properly decontaminating the observed diagrams from background/foreground disc stars and other sources. On the other hand, CMDs were also obtained based upon star selection in proper motion diagrams. Taking into account our deep CMDs and LFs analyses, we find that 17 out of 22 new GC candidates may be real and should therefore be followed-up, while 5 candidates were discarded from the original sample. We also search for RR Lyrae and Mira variable stars in the fields of these new GC candidates. In particular, we confirm that Minni 40 may be a real cluster. If confirmed by further follow-up analysis, it would be the closest GC to the Galactic centre in projected angular distance, located only 0.5 deg away from it. We consider that it is very difficult to confirm the physical reality of these small, poorly-populated bulge GCs so in many cases alternative techniques are needed to corroborate our findings.
The discovery of very distant stars in the halo of the Milky Way provides valuable tracers on the Milky Way mass and its formation. Beyond 100 kpc from the Galactic center, most of the stars are likely to be in faint dwarf galaxies or tidal debris from recently accreted dwarfs, making the outer reaches of the Galaxy important for understanding the Milky Ways accretion history. However, distant stars in the halo are scarce. In that context, RR Lyrae are ideal probes of the distant halo as they are intrinsically bright and thus can be seen at large distances, follow well-known period-luminosity relations that enable precise distance measurements, and are easily identifiable in time-series data. Therefore, a detailed study of RR Lyrae will help us understand the accreted outskirts of the Milky Way. In this contribution, we present the current state of our systematic search for distant RR Lyrae stars in the halo using the DECam imager at the 4m telescope on Cerro Tololo (Chile). The total surveyed area consists of more than 110 DECam fields (~ 350 sq. deg) and includes two recent independent campaigns carried out in 2017 and 2018 with which we have detected > 650 candidate RR Lyrae stars. Here we describe the methodology followed to analyze the two latest campaigns. Our catalog contains a considerable number of candidate RR Lyrae beyond 100 kpc, and reaches out up to ~ 250 kpc. The number of distant RR Lyrae found is consistent with recent studies of the outer halo. These stars provide a set of important probes of the mass of the Milky Way, the nature of the halo, and the accretion history of the Galactic outskirts.
The most common methods to derive the distance to globular clusters using RR Lyrae variables are reviewed, with a special attention to those that have experienced significant improvement in the past few years. From the weighted average of these most recent determinations the absolute magnitude of the RR Lyrae stars at [Fe/H]=-1.5 is Mv = 0.59 +/- 0.03 mag, corresponding to a distance modulus for the LMC (m-M)o = 18.48 +/- 0.05.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
