Kyle M. Cudworth

The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters

We validate the accuracy and precision of the current SEGUE (Sloan Extension for Galactic Understanding and Exploration) Stellar Parameter Pipeline (SSPP), which determines stellar atmospheric parameters (effective temperature, surface gravity, and metallicity) and radial velocities (RVs), by comparing these estimates for selected members of three globular clusters (M 13, M 15, and M 2) and two open clusters (NGC 2420 and M 67) to the literature values. Spectroscopic and photometric data obtained during the course of the original Sloan Digital Sky Survey (SDSS-I) and its first extension (SDSS-II/SEGUE) are used to determine atmospheric parameter and RV estimates for stars in these clusters. Based on the scatter in the metallicities derived for the members of each cluster, we quantify the typical uncertainty of the SSPP values, σ ([Fe/H]) = 0.13 dex for stars in the range of –0.3 ≤ g – r ≤ 1.3 and 2.0 ≤ log g ≤ 5.0, at least over the metallicity interval spanned by the clusters studied (–2.3 ≤ [Fe/H] ≤ 0). The surface gravities and effective temperatures derived by the SSPP are also compared with those estimated from the comparison of color-magnitude diagrams with stellar evolution models; we find satisfactory agreement (σ(T eff)< 200 K and σ(log g) ≤ 0.4 dex).

Target selection for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution infrared spectroscopic survey spanning all Galactic environments (i.e., bulge, disk, and halo), with the principal goal of constraining dynamical and chemical evolution models of the Milky Way. APOGEE takes advantage of the reduced effects of extinction at infrared wavelengths to observe the inner Galaxy and bulge at an unprecedented level of detail. The surveys broad spatial and wavelength coverage enables users of APOGEE data to address numerous Galactic structure and stellar populations issues. In this paper we describe the APOGEE targeting scheme and document its various target classes to provide the necessary background and reference information to analyze samples of APOGEE data with awareness of the imposed selection criteria and resulting sample properties. APOGEEs primary sample consists of ~105 red giant stars, selected to minimize observational biases in age and metallicity. We present the methodology and considerations that drive the selection of this sample and evaluate the accuracy, efficiency, and caveats of the selection and sampling algorithms. We also describe additional target classes that contribute to the APOGEE sample, including numerous ancillary science programs, and we outline the targeting data that will be included in the public data releases.

A Matched-Filter Analysis of the Tidal Tails of the Globular Cluster Palomar 5

The tidal tails of the globular cluster Palomar 5 are analyzed over a 41 deg2 area of the Sloan Digital Sky Survey photometric catalogs. The matched filter algorithm provides the maximum possible signal-to-noise detection of the cluster stars over the measured background, and the expected and actual effectiveness of the technique in the context of this data set is discussed. The stellar background is examined in some detail for systematic variation as a function of Galactic position in order to assess its effect on the detection efficiency. Of the total number of Pal 5 stars detected, 45% are out in the tails. The tails are found as the only additional 3 σ overdensity of cluster stars over the entire 41 deg2 area studied. The annular-averaged density of stars along the tails is fitted to a power law in radius with best-fit index -1.58 ± 0.07, significantly steeper than that predicted from a constant orbit-averaged mass-loss rate.

Radial velocities of stars in the globular cluster M4 and the cluster distance

The internal stellar velocity distribution of the globular cluster M4 is evaluated from nearly 200 new radial velocity measurements good to 1 km/s and a rederivation of existing proper motions. The mean radial velocity of the cluster is 70.9 +/- 0.6 km/s. The velocity dispersion is 3.5 +/- 0.3 km/s at the core, dropping marginally towards the outskirts. Such a low internal dispersion is somewhat at odds with the clusters orbit, for which the perigalacticon is sufficiently close to the galactic center that the probability of cluster disruption is high; a tidal radius two-thirds the currently accepted value would eliminate the discrepancy. The cluster mass-to-light ratio is also small, M/L(sub V) = 1.0 +/- 0.4 in solar units. M4 thus joins M22 as a cluster of moderate and concentration with a mass-to-light ratio among the lowest known. The astrometric distance to the cluster is also smaller than expected, 1.72 +/- 0.14 kpc. This is only consistent with conventional estimates of the luminosity of horizontal branch stars provided an extinction law R = A(sub V)/E(B-V) approximately 4 is adopted, as has been suggested recently by several authors.

Proper motions, membership, and photometry of open clusters near Eta Carinae

Proper motions and photographic photometry have been derived for nearly 600 stars with 7.5 < V < 15.5 in the region of the very young open clusters Tr 14, Tr 16, and Cr 232 based on 26 plates dating from 1893 to 1990. Cluster membership probabilities have been derived from the proper motions and color-magnitude diagrams of probable members of each cluster are presented. In contrast to a few of the previous studies we find all three clusters to lie at the same distance

Astrometry of Star Clusters: Problems, Techniques, and Opportunities

The astrophysical problems that can be attacked via proper motions in star clusters are set forth and current techniques and opportunities are described. Cluster membership work continues to progress with recent work mixing plates from various telescopes, including large reflectors. More and better internal motion studies are needed to have a significant impact on the dynamical models. Absolute proper motions of clusters present a very difficult problem, but for globulars, at least, the data are desperately needed.

Dynamical Modeling of M13 Proper Motions

Proper motion data of Ml3 cluster members are very useful for the investigation of the cluster’s internal dynamics. We introduce a maximum likelihood method to fit these data in terms of conventional King-Michie models.