Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Milky Ways circular velocity curve and its constraint on the Galactic mass with RR Lyrae stars
49
0
0.0
(
0
)
Authors
Iminhaji Ablimit
Ask ChatGPT about the research
No Arabic abstract
We present a sample of 1148 ab-type RR Lyrae (RRLab) variables identified from Catalina Surveys Data Release 1, combined with SDSS DR8 and LAMOST DR4 spectral data. We firstly use a large sample of 860 Galactic halo RRLab stars and derive the circular velocity distributions for the stellar halo. With the precise distances and carefully determined radial velocities (the center-of-mass radial velocities) by considering the pulsation of the RRLab stars in our sample, we can obtain a reliable and comparable stellar halo circular velocity curve. We take two different prescriptions for the velocity anisotropy parameter {beta} in the Jeans equation to study the circular velocity curve and mass profile. We test two different solar peculiar motions in our calculation. Our best result with the adopted solar peculiar motion 1 of (U, V, W) = (11.1, 12, 7.2) km/s is that the enclosed mass of the Milky Way within 50 kpc is (3.75 +/- 1.33) *10^11Msun based on beta = 0 and the circular velocity 180 +/- 31.92 (km/s) at 50 kpc. This result is consistent with dynamical model results, and it is also comparable to the previous similar works.
rate research
Read More
We measure the Milky Ways rotation curve over the Galactocentric range 4 kpc <~ R <~ 14 kpc from the first year of data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We model the line-of-sight velocities of 3,365 stars in fourteen fields with b = 0 deg between 30 deg < l < 210 deg out to distances of 10 kpc using an axisymmetric kinematical model that includes a correction for the asymmetric drift of the warm tracer population (sigma_R ~ 35 km/s). We determine the local value of the circular velocity to be V_c(R_0) = 218 +/- 6 km/s and find that the rotation curve is approximately flat with a local derivative between -3.0 km/s/kpc and 0.4 km/s/kpc. We also measure the Suns position and velocity in the Galactocentric rest frame, finding the distance to the Galactic center to be 8 kpc < R_0 < 9 kpc, radial velocity V_{R,sun} = -10 +/- 1 km/s, and rotational velocity V_{phi,sun} = 242^{+10}_{-3} km/s, in good agreement with local measurements of the Suns radial velocity and with the observed proper motion of Sgr A*. We investigate various systematic uncertainties and find that these are limited to offsets at the percent level, ~2 km/s in V_c. Marginalizing over all the systematics that we consider, we find that V_c(R_0) < 235 km/s at >99% confidence. We find an offset between the Suns rotational velocity and the local circular velocity of 26 +/- 3 km/s, which is larger than the locally-measured solar motion of 12 km/s. This larger offset reconciles our value for V_c with recent claims that V_c >~ 240 km/s. Combining our results with other data, we find that the Milky Ways dark-halo mass within the virial radius is ~8x10^{11} M_sun.
We have used photometric data on almost 91 000 fundamental-mode RR Lyrae stars (type RRab) detected by the OGLE survey to investigate properties of old populations in the Milky Way. Based on their metallicity distributions, we demonstrate that the Galaxy is built from three distinct old components: halo, bulge, and disk. The distributions reach their maxima at approximately [Fe/H]_J95 = -1.2, -1.0, and -0.6 dex on the Jurcsiks metallicity scale, respectively. We find that, very likely, the entire halo is formed from infalling dwarf galaxies. It is evident that halo stars penetrate the inner regions of the Galactic bulge. We estimate that about one-third of all RR Lyr stars within the bulge area belong in fact to the halo population. The whole old bulge is dominated by two populations, A and B, represented by a double sequence in the period-amplitude (Bailey) diagram. The boundary in iron abundance between the halo and the disk population is at about [Fe/H]_J95 = -0.8 dex. Using Gaia DR2 for RRab stars in the disk area, we show that the observed dispersion of proper motions along the Galactic latitude decreases smoothly with the increasing metal content excluding a bump around [Fe/H]_J95 = -1.0 dex.
Most of known RR Lyraes are type ab RR Lyraes (RRLab), and they are the excellent tool to map the Milky Way and its substructures. We find that 1148 RRLab stars determined by Drake et al.(2013) have been observed by spectroscopic surveys of SDSS and LAMOST. We derived radial velocity dispersion, circular velocity and mass profile from 860 halo tracers in our paper I. Here, we present the stellar densities and radial velocity distributions of thick disk and halo of the Milky Way. The 288 RRLab stars located in the thick disk have the mean metallicity of [Fe/H]$=-1.02$. Three thick disk tracers have the radial velocity lower than 215 km $rm s^{-1}$. With 860 halo tracers which have a mean metallicity of [Fe/H]$=-1.33$, we find a double power-law of $n(r) propto r^{-2.8}$ and $n(r) propto r^{-4.8}$ with a break distance of 21 kpc to express the halo stellar density profile. The radial velocity dispersion at 50 kpc is around 78 km $rm s^{-1}$.
We collected the largest spectroscopic catalog of RR Lyrae (RRLs) including $approx$20,000 high-, medium- and low-resolution spectra for $approx$10,000 RRLs. We provide the analytical forms of radial velocity curve (RVC) templates. These were built using 36 RRLs (31 fundamental -- split into three period bins -- and 5 first overtone pulsators) with well-sampled RVCs based on three groups of metallic lines (Fe, Mg, Na) and four Balmer lines (H$_alpha$, H$_beta$, H$_gamma$, H$_delta$). We tackled the long-standing problem of the reference epoch to anchor light curve and RVC templates. For the $V$-band, we found that the residuals of the templates anchored to the phase of the mean magnitude along the rising branch are $sim$35% to $sim$45% smaller than those anchored to the phase of maximum light. For the RVC, we used two independent reference epochs for metallic and Balmer lines and we verified that the residuals of the RVC templates anchored to the phase of mean RV are from 30% (metallic lines) up to 45% (Balmer lines) smaller than those anchored to the phase of minimum RV. We validated our RVC templates by using both the single- and the three-phase points approach. We found that barycentric velocities based on our RVC templates are two-three times more accurate than those available in the literature. We applied the current RVC templates to Balmer lines RVs of RRLs in the globular NGC~3201 collected with MUSE at VLT. We found the cluster barycentric RV of $V_{gamma}$=496.89$pm$8.37(error)$pm$3.43 (standard deviation) km/s, which agrees well with literature estimates.
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.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
