Publications of the Astronomical Society of the Pacific

Cowley, Anne P.; Hartwick, F. David A.

doi: 10.1086/499387pmid: N/A

Johnson, Christian I.; Kraft, Robert P.; Pilachowski, Catherine A.; Sneden, Christopher; Ivans, Inese I.; Benman, Gabriel

doi: 10.1086/497435pmid: N/A

We have derived sodium, magnesium, and aluminum abundances for more than 100 red giant branch (RGB) stars in each of the Galactic globular clusters M3 and M13 (235 total stars), using moderate resolution (R∼10,000) spectra obtained with the 3.5 m WIYN telescope and Hydra multifiber spectrograph. Temperatures for the cluster samples are based on calibrations of photometric indices, in particular V - K. Gravities, microturbulent velocities, and the overall M3 and M13 metallicities ([Fe/H] ∼-1.50) are based on the results of previous work by the Lick‐Texas group. Na and Mg abundances have been determined from observed versus synthetic spectrum matches of the Na i λλ5682, 5688 lines and the Mg i λ5711 line. Al abundances have been determined from equivalent‐width measurements of the Al i (λλ6696, 6698) doublet. The resulting M3 and M13 analyses are compared with the more detailed high‐resolution analyses of smaller samples of RGB stars. We conclude that on average, M13 tends to have higher abundances of Na, Mg, and Al than M3 by roughly 0.10–0.20 dex, a likely by‐product of additional proton‐capture synthesis. Compared to halo field stars of comparable [Fe/H] metallicity, M3 and M13 giants tend to have a greater abundance of Na for a given Mg. Unlike M3, the most luminous M13 giants (M0v<-1.70) show a strong inclination toward having [Na/Fe] values enhanced above the cluster median. In the last 0.70 mag interval before M13’s RGB tip, there is a large number of low‐O, high‐Na, and high‐Al stars. This is not seen in M3. Compared with halo field giants, the anomalous abundances of O, Na, Mg, and Al seen in both M3 and M13 stars appear to have a “primordial” (“pollution”?) origin. However, a “second stage” of proton‐capture synthesis within the M13 giants themselves seems required to distinguish their pattern of O, Na, Mg, and Al abundances from those of the brightest giants of M3.

Stetson, Peter B.; Catelan, M.; Smith, Horace A.

doi: 10.1086/497302pmid: N/A

New BVRI broadband photometry and astrometry are presented for the globular cluster NGC 4147, based upon measurements derived from 524 ground‐based CCD images mostly either donated by colleagues or retrieved from public archives. We have also reanalyzed five exposures of the cluster obtained with WFPC2 on the Hubble Space Telescope in the F439W and F555W (B and V) filters. We present calibrated color‐magnitude and color‐color diagrams. Analysis of the color‐magnitude diagram reveals morphological properties generally consistent with published metal‐abundance estimates for the cluster, and an age typical of other Galactic globular clusters of similar metallicity. We have also redetermined the periods and mean magnitudes for the RR Lyrae variables, including a new c‐type variable reported here for the first time. Our data do not show clear evidence for photometric variability in candidate V18, recently reported by Arellano Ferro et al. (2004, Rev. Mex. A&A, 40, 209). These observations also support the nonvariable status of candidates V5, V9, and V15. The union of our light‐curve data with those of Newburn (1957, AJ, 62, 197), Mannino (1957, Mem. Soc. Astron. Italiana, 28, 285), and Arellano Ferro et al. (op. cit.) permits the derivation of significantly improved periods. The mean periods and the Bailey period‐amplitude diagrams support the classification of the cluster as Oosterhoff I, despite its predominantly blue horizontal branch. The number ratio of c‐ to ab‐type RR Lyrae stars, on the other hand, is unusually high for an Oosterhoff I cluster. The calibrated results have been made available through the first author’s Web site.

Rutkowski, Artur; Waniak, Wacław

doi: 10.1086/497157pmid: N/A

We present 36 observations of 17 visual binaries of moderate separation (ranging from 0.″15 to 0.″790) made with the 50 cm Cassegrain telescope of the Jagiellonian University in Kraków. The speckle interferometry technique was combined with modest optical hardware and a standard photometric CCD camera. We used broadband VRI filters without a Risley prism to reduce differential color refraction. Thus, we performed a model analysis to investigate the influence of this effect on the results of the measurements. For binary components of spectral type O–F, the difference of three spectral classes between them should bias their relative positions by no more than a couple of tens of milliarcseconds (mas) for moderate zenith distances. The statistical analysis of our results confirmed this conclusion. A cross‐spectrum approach was applied to resolve the quadrant ambiguity. Our separations have rms deviations of 0.″012, and our position angles have rms deviations of 1.°8. Relative photometry in V, R, and I filters appeared to be the less accurately determined parameter. We discuss our errors in detail and compare them to other speckle data. This comparison clearly shows the quite good accuracy of our measurements. We also present an example of the enhancement of image resolution for an extended object with an angular size that is greater than the atmospheric coherence patch, using speckle interferometry techniques.

Cortes, Stephanie R.; King, Jeremy R.

doi: 10.1086/498457pmid: N/A

We use an SX Phe period‐luminosity relation to derive distance estimates and Galactic kinematic parameters for the short‐period pulsating blue metal‐poor stars CS 29499−057 and CS 22966−043. The resulting kinematics are quite distinctive relative to the metal‐poor halo field. Even though these two field blue stragglers’ binarity is consistent with the idea of formation in a mass transfer system, we speculate that these stars’ origin instead lies in a Galactic merger or interaction with a dwarf galaxy satellite, or in the merger of a stellar binary system. The former possibility is consistent with CS 22966−043’s significant [α/Fe] deficiency. A non–mass‐transfer origin for both binaries is also consistent with (though not necessarily precluded by) the lack of any significant s‐process enhancement seen in either star, and the long orbital period of CS 29499−057 that may preclude a mass transfer origin. In an effort to determine distances to additional blue metal‐poor stars, we have photometrically monitored CS 22890−069, CS 22872−062, and CS 22884−065. However, the light curves of these three objects indicate no short‐period photometric variability at the level of a few hundredths of a magnitude.

Wellhouse, Joseph W.; Hoard, D. W.; Howell, S. B.; Wachter, Stefanie; Esin, A. A.

doi: 10.1086/497084pmid: N/A

Our understanding of the formation and evolution of magnetic cataclysmic variables from initially detached, post–common‐envelope binary stars containing a magnetic white dwarf and a main‐sequence star is currently poorly constrained, due to the lack of observational identification of the progenitor systems. Very few potential pre–cataclysmic variables containing a magnetic white dwarf are known, compared with ≈25% of the cataclysmic variable population that contain magnetic white dwarfs. We present the results of a search for candidate binary systems containing a magnetic white dwarf, which utilized photometric data from the Two Micron All Sky Survey (2MASS; as well as Hubble Space Telescope and WIYN Observatory follow‐up data for several objects). Our target sample was drawn primarily from the comprehensive list of magnetic white dwarfs by Wickramasinghe & Ferrario, plus several recently identified objects selected from the literature. Out of 51 2MASS detections, no convincing binary candidates were found. However, six objects merit additional observation to determine the origin of a small near‐infrared excess that could be attributed to a very low mass stellar or substellar companion. An additional four white dwarfs are possibly at the centers of previously unknown, and likely unresolved, planetary nebulae.

Peters, Christopher S.; Thorstensen, John R.

doi: 10.1086/497384pmid: N/A

We present spectroscopy of four cataclysmic variables. Using radial velocity measurements, we find orbital periods Porb for the first time: for GY Hya, 0.347230(9) days, for SDSS J204448−045929, 1.68(1) days, for V392 Hya, 0.324952(5) days, and for RX J1951.7+3716, 0.492(1) days. We also detect the spectra of the secondary stars, estimate their spectral types, and derive distances based on surface brightness and Roche lobe constraints.

Kim, Seung‐Lee; Lee, Jae Woo; Kim, Chulhee; Lee, Chung‐Uk; Kang, Yong Beom; Koo, Jae‐Rim

doi: 10.1086/497623pmid: N/A

We present BV photometric results of the variable star LZ Her. Frolov & Irkaev classified it as a field SX Phe–type pulsating star, but our observations clearly show that LZ Her is not an SX Phe star, but rather a W UMa–type eclipsing binary, as reported by Garrido et al. The orbital period is derived to be 0.33173646 days by combining our data with that in the literature. The eclipsing light‐curve solution from the Wilson‐Devinney code shows that LZ Her belongs to the W subgroup of W UMa stars; the primary component is less massive and hotter, with a spectral type of F9–G0, and the secondary is more massive and cooler, with a spectral type G5–G6. The spectral types were estimated from the photometric light‐curve solution. Asymmetric light curves could be explained by assuming a cool spot on the secondary star. In the observing field of LZ Her, we found a new eclipsing binary, 2MASS 17500367+2928020, with an orbital period of 0.3056 days.

Rosolowsky, E.

doi: 10.1086/497582pmid: N/A

We reanalyze the catalogs of molecular clouds in the Local Group to determine the parameters of their mass distributions in a uniform manner. The analysis uses the error‐in‐variables method of parameter estimation, which accounts not only for the variance of the sample when drawn from a parent distribution, but also for errors in the mass measurements. Testing the method shows that it recovers the underlying properties of cumulative mass distribution without bias while accurately reflecting uncertainties in the parameters. Clouds in the inner disk of the Milky Way follow a truncated power‐law distribution with index γ = -1.5 ± 0.1 and maximum mass of 106.5 M⊙. The distributions of cloud mass for the outer Milky Way and M33 show significantly steeper indices (γOMW = -2.1 ± 0.2 and γM33 = -2.9 ± 0.4, respectively), with no evidence of a cutoff. The mass distribution of clouds in the Large Magellanic Cloud has a marginally steeper distribution than the inner disk of the Milky Way (γ = -1.7 ± 0.2) and also shows evidence of a truncation, with a maximum mass of 106.5 M⊙. The mass distributions of molecular clouds vary dramatically across the Local Group, even after accounting for the systematic errors that arise in comparing heterogeneous data and catalogs. These differences should be accounted for in studies that aim to reproduce the molecular cloud mass distributions, or in studies that use the mass spectrum as a parameter in a model.

Fabricant, Daniel; Fata, Robert; Roll, John; Hertz, Edward; Caldwell, Nelson; Gauron, Thomas; Geary, John; McLeod, Brian; Szentgyorgyi, Andrew; Zajac, Joseph; Kurtz, Michael; Barberis, Jack; Bergner, Henry; Brown, Warren; Conroy, Maureen; Eng, Roger;