ABSTRACT Using the example of the tidal stream of the Milky Way globular cluster Palomar 5 (Pal 5), we demonstrate how observational data on tidal streams can be efficiently reduced in dimensionality ...and modeled in a Bayesian framework. Our approach combines detection of stream overdensities by a Difference-of-Gaussians process with fast streakline models of globular cluster streams and a continuous likelihood function built from these models. Inference is performed with Markov chain Monte Carlo. By generating model streams, we show that the unique geometry of the Pal 5 debris yields powerful constraints on the solar position and motion, the Milky Way and Pal 5 itself. All 10 model parameters were allowed to vary over large ranges without additional prior information. Using only readily available SDSS data and a few radial velocities from the literature, we find that the distance of the Sun from the Galactic Center is 8.30 0.25 kpc, and the transverse velocity is 253 16 km s−1. Both estimates are in excellent agreement with independent measurements of these two quantities. Assuming a standard disk and bulge model, we determine the Galactic mass within Pal 5's apogalactic radius of 19 kpc to be . Moreover, we find the potential of the dark halo with a flattening of to be essentially spherical-at least within the radial range that is effectively probed by Pal 5. We also determine Pal 5's mass, distance, and proper motion independently from other methods, which enables us to perform vital cross-checks. Our inferred heliocentric distance of Pal 5 is kpc, in perfect agreement with, and more precise than, estimates from isochrone fitting of deep Hubble Space Telescope (HST) imaging data. We conclude that finding and modeling more globular cluster streams is an efficient way to map out the structure of our Galaxy to high precision. With more observational data and by using additional prior information, the precision of this mapping can be significantly increased.
We report the discovery of 13 confirmed two-image quasar lenses from a systematic search for gravitationally lensed quasars in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). We adopted ...a methodology similar to that used in the SDSS Quasar Lens Search (SQLS). In addition to the confirmed lenses, we report 11 quasar pairs with small angular separations ( ≲ 2 arcsec) confirmed from our spectroscopy, which are either projected pairs, physical binaries, or possibly quasar lens systems whose lens galaxies have not yet been detected. The newly discovered quasar lens system, SDSS J1452+4224 at z
s ≈ 4.8 is one of the highest redshift multiply imaged quasars found to date. Furthermore, we have over 50 good lens candidates yet to be followed up. Owing to the heterogeneous selection of BOSS quasars, the lens sample presented here does not have a well-defined selection function.
Studies of Galactic chemical, and dynamical evolution in the solar neighborhood depend on the availability of precise atmospheric parameters (effective temperature Tsubeff , metallicity Fe/H, and ...surface gravity log g) for solar-type stars. In this work, we use an alternative method based on spectral indices to determine the atmospheric parameters of a sample of nearby FGK dwarfs and sub-giants observed by the MARVELS survey at moderate resolving power. To avoid a time-consuming manual analysis, we have developed three codes to automatically normalize the observed spectra, measure the equivalent widths of the indices, and, through a comparison of those with values calculated with predetermined calibrations, estimate the atmospheric parameters of the stars. Our approach was able to recover the parameters within 80 K for Tsubeff, 0.05 dex for Fe/H, and 0.15 dex for log g, values that are lower than or equal to the typical external uncertainties found between different high-resolution analysis. The results show that the spectral indices are a competitive tool to characterize stars with intermediate resolution spectra.
Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. Here we make a forecast of the expected stellar ...sample resulting from the Dark Energy Survey (DES) and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 X 108 stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy. DES will probe low-mass stellar and sub-stellar objects at depths from three to eight times larger than those in the Sloan Digital Sky Survey (SDSS). The faint end of the main sequence (MS) will be densely sampled beyond 10 kpc. The slope of the low mass end of the stellar initial mass function (IMF) will be constrained to within a few hundredths of dex, even in the thick disk and halo. In the sub-stellar mass regime, the IMF slope will be potentially constrained to within dlog (m)/dlog m 0.1. About 3 X 104 brown dwarf candidates and at least 7.6 X 105 white dwarf candidates will be selected, the latter embedded into the thick disk and halo, for future follow-up. The stellar halo flattening will also be constrained to within a few percent. DES will probe the MS of new Milky Way satellites and halo clusters for distances out to 120 kpc, therefore yielding stellar surface density contrasts 1.6-1.7 times larger than those attainable with SDSS. It will also allow detection of these objects in the far reaches of the stellar halo, substantially increasing the number and quality of probes to the Galactic potential. Combined with northern samples, such as the SDSS, the DES stellar sample will yield constraints on the structure and stellar populations of Galactic components in unprecedented detail. In particular, the combined sample from both hemispheres will allow detailed studies of halo and thick disk asymmetries and triaxiality.
Context. Determining distances to individual field stars is a necessary step towards mapping Galactic structure and determining spatial variations in the chemo-dynamical properties of stellar ...populations in the Milky Way. Aims. In order to provide stellar distance estimates for various spectroscopic surveys, we have developed a code that estimates distances to stars using measured spectroscopic and photometric quantities. We employ a Bayesian approach to build the probability distribution function over stellar evolutionary models given these data, delivering estimates of model parameters (including distances) for each star individually. Our method provides several alternative distance estimates for each star in the output, along with their associated uncertainties. This facilitates the use of our method even in the absence of some measurements. Methods. The code was first tested on simulations, successfully recovering input distances to mock stars with ≲1% bias. We found the uncertainties scale with the uncertainties in the adopted spectro-photometric parameters. The method-intrinsic random distance uncertainties for typical spectroscopic survey measurements amount to around 10% for dwarf stars and 20% for giants, and are most sensitive to the quality of log g measurements. Results. The code was then validated by comparing our distance estimates to parallax measurements from the Hipparcos mission for nearby stars (<300 pc), to asteroseismic distances of CoRoT red giant stars, and to known distances of well-studied open and globular clusters. The photometric data of these reference samples cover both optical and infrared wavelengths. The spectroscopic parameters are also based on spectra taken at various wavelengths, with varying spectral coverage and resolution: the Sloan Digital Sky Survey programs SEGUE and APOGEE, as well as various ESO instruments. Conclusions. External comparisons confirm that our distances are subject to very small systematic biases with respect to the fundamental Hipparcos scale (+ 0.4% for dwarfs, and + 1.6% for giants). The typical random distance scatter is 18% for dwarfs, and 26% for giants. For the CoRoT-APOGEE sample, which spans Galactocentric distances of 4−14 kpc, the typical random distance scatter is ≃15% both for the nearby and farther data. Our distances are systematically larger than the CoRoT distances by about + 9%, which can mostly be attributed to the different choice of priors. The comparison to known distances of star clusters from SEGUE and APOGEE has led to significant systematic differences for many cluster stars, but with opposite signs and substantial scatter. Finally, we tested our distances against those previously determined for a high-quality sample of giant stars from the RAVE survey, again finding a small systematic trend of + 5% and an rms scatter of 30%. Efforts are underway to provide our code to the community by running it on a public server.
The tidal tails of NGC 2298 Balbinot, Eduardo; Santiago, Basílio X.; da Costa, Luiz N. ...
Monthly notices of the Royal Astronomical Society,
September 2011, Volume:
416, Issue:
1
Journal Article
Peer reviewed
We present an implementation of the matched-filter technique to detect tidal tails of globular clusters. The method was tested using the Sloan Digital Sky Survey (SDSS) data for the globular cluster ...Palomar 5 revealing its well-known tidal tails. We also ran a simulation of a globular cluster with a tidal tail where we successfully recover the tails for a cluster at the same position and with the same characteristics of NGC 2298. Based on the simulation we estimate that the matched-filter increases the contrast of the tail relative to the background of stars by a factor of 2.5 for the case of NGC 2298. We also present the photometry of the globular cluster NGC 2298 using the MOSAIC2 camera installed on the Cerro Tololo International Observatory (CTIO) 4-m telescope. The photometry covers ∼3 deg2 reaching V∼ 23. A fit of a King profile to the radial density profile of NGC 2298 shows that this cluster has a tidal radius of
which is twice as in the literature. The application of the matched-filter to NGC 2298 reveals several extra-tidal structures, including a leading and trailing tail. We also find that NGC 2298 has extra-tidal structures stretching towards and against the Galactic disc, suggesting strong tidal interaction. Finally, we assess how the matched-filter performs when applied to a globular cluster with and without mass segregation taken into account. We find that disregarding the effects of mass segregation may significantly reduce the detection limit of the matched-filter.
Abstract
We report the characterization of the first 62 Mapping Nearby Galaxies at the Apache Point Observatory active galactic nuclei (AGNs) hosts and the definition of a control sample of ...non-active galaxies. This control sample was selected in order to match the AGN hosts in terms of stellar mass, redshift, visual morphology and inclination. The stellar masses are in the range $9.4<\mbox{log}\left(\mathrm{{M}/M}_{\odot }\right)<11.5$, and most objects have redshifts ≤0.08. The AGN sample is mostly comprised low-luminosity AGN, with only 17 ‘strong AGN’ with $L(\rm {O\, \small {III}}\lambda 5007\, {^{\circ}_{\rm A}})\ge {3.8}\times 10^{40}\, \mbox{erg}\, \mbox{s}^{-1}$. The inner 1–3 kpc of the control sample galaxies are dominated by the oldest (≥ 4 Gyr) component, with a small contribution of intermediate age and young stars (<940 Myr). Examining the relationship between the stellar population properties and $L(\rm {O\, \small {III}})$, we find that with increasing $L(\rm {O\, \small {III}})$, the AGN exhibit a decreasing contribution from the oldest stellar population relative to control galaxies and an increasing contribution from the younger components (∼40 Myr). We also find a correlation of the mean age differences (AGN–control) with $L(\rm {O\, \small {III}})$, in the sense that more luminous AGNs are younger than the control objects, while the low-luminosity AGNs are older. These results support a connection between the growth of the galaxy bulge via formation of new stars and the growth of the Supermassive Black Hole via accretion in the AGN phase.
We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity ...Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Kepierian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695 super(+0.0188) sub(0.0187) days, an eccentricity of 0.4375 + or - 0.0040, and a semi-amplitude of 2948.14 super(+16.65) sub(-16.55) m s super(-1). Using additional high-resolution spectroscopy, we find the host star has an effective temperature T sub(eff) = 6004 + or - 34 K, a surface gravity log g (cgs) = 4.55 + or - 0.17, and a metallicity Fe/H = +0.04 + or - 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 + or - 0.09 M sub(odot) and 0.92 + or - 0.19 R sub(odot). The minimum mass of MARVELS-5b is 65.0 + or - 2.9 M sub(Jup), indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 + or - 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M sub(odot) at a separation larger than 40 AU.
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