Michael M. Shara

A CATALOG AND ATLAS OF CATACLYSMIC VARIABLES-SECOND EDITION

We present a catalog of all 1020 known cataclysmic variables (CVs). This paper is a major update of the first edition of the catalog (Downes and Shara 1993, PASP, 105, 127), which contained coordinates (measured in the reference frame of the Hubble Space Telescope Guide Star Survey for the non-novae, and obtained from the literature for the novae), the variability type, the magnitude range, and references to both finding charts and spectroscopy. Also included in the catalog were finding charts for all dwarf novae, novalike variables, and objects classified only as cataclysmic variables known as of 1993; a similar catalog and atlas for novae has been published by Duerbeck (1978a). This updated edition includes 195 new objects (172 CVs and 23 non-CVs), revised identifications for 57 objects, and revised information (classification and spectral references) when available. We also now include plate identification information for the coordinate measurements, a reference to the classification, proper motion information where appropriate, and a table showing the CVs observed by space-based observatories. This second edition is inclusive of the first edition, although only new or updated charts are presented.

Oscillating Blue Stragglers in the Core of 47 Tucanae

Six SX Phe variables detected in a 39 hr time series of Hubble Space Telescope Planetary Camera exposures in the F336W (U) filter are discussed. Two of these stars show both the fundamental and first-overtone modes and are among the first double-mode SX Phe stars reported in globular clusters. One of the double-mode stars shows evidence for a third mode near the expected period for the second overtone. Two of the other SX Phe variables in 47 Tuc are shown to oscillate simultaneously in the fourth and fifth radial overtones. The remaining two variables both have multiple oscillations excited which include nonradial modes. To support interpretation of these variables we provide evolutionary computations using current opacities and physics allowing comparison of the blue straggler stars (BSSs) and several cluster-magnitude diagram features for 47 Tuc. Linear nonadiabatic oscillation analysis is performed for a significant range of envelope and full evolutionary models in order to (1) establish the theoretical characteristics of SX Phe pulsations (e.g., location of primary driving and adiabatic nature), (2) establish the theoretical red and blue edges of the instability strip, and (3) derive the theoretical relations necessary for obtaining evolutionary and pulsational masses. Masses inferred from fundamental period-period ratio relations for the double-mode oscillators are well above the turnoff mass in 47 Tucanae and are consistent with expected masses for these blue stragglers based on position in the color-magnitude diagram (CMD) and comparison with theoretical evolutionary tracks. Combining the evolution and pulsation constraints results in mass estimates for the four double-mode BSSs in 47 Tuc of M = 1.35 ± 0.1 to 1.6 ± 0.2 M☉.

Hubble Space Telescope Detection of Optical Companions of WR 86, WR 146, and WR 147: Wind Collision Model Confirmed

Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of the rado-binary Wolf-Rayet stars WR 146 and WR 147, as well as the 02 visual binary WR 86, resolve each of them into two very close optical components. The colors of these optical pairs are similar, indicating that they are likely to be physically bound WR + OB systems at the same distance. Comparison of the locations of the optical components of WR 146 and WR 147 with high-resolution radio maps strikingly demonstrates that the nonthermal radio components arise between the optical binary components, closer to the OB component than the WR. This is as expected if the nonthermal radio emission results from the collision of the stellar winds of the binary components seen in the HST images. The similar magnitudes and colors determined for the components of WR 86 from our HST images, combined with an analysis of the unresolved, combined WC7 + OB optical spectrum, indicates an absolute magnitude for the WC7 component of about MV ~ -5.

Two Groups of Nearly Coeval Star Clusters in the Small Magellanic Cloud

We report new photometry and main-sequence turnoff ages for seven populous star clusters in the SMC with MV < -6 and age greater than 1 Gyr, using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. In contrast to the accepted picture, these clusters appear to have formed in two brief intervals, the oldest 8 ± 2 Gyr ago and one during a more recent burst 2 ± 0.5 Gyr ago. When the ridgelines of the four clusters (NGC 339, 361, and 416 and Kron 3) in the 8 Gyr burst are aligned, the dispersion in turnoff luminosities is less than 0.2 mag, corresponding to a maximum age spread of ±0.7 Gyr. When the ridgelines of three clusters (NGC 152, 411, and 419) in the 2 Gyr burst are aligned, the maximum dispersion of 0.2 mag in turnoff luminosity corresponds to a permitted age spread of ±0.2 Gyr. Within each group of clusters, the entire cluster loci (including red giant branches and clumps) are nearly identical, consistent with a very small spread in metallicity and age. In contrast to the wide dispersion in ages previously reported in the literature, our sample with more precise photometry and age measurements supports a burst-punctuated rather than a continuous cluster formation history for the oldest SMC clusters.

Cataclysmic and Close Binaries in Star Clusters. IV. the Unexpectedly Low Number of Erupting Dwarf Novae Detected by the Hubble Space Telescope in the Core of 47 Tucanae

The standard model of tidal capture predicts that D45 moderately bright cataclysmic binaries should exist today in 47 Tuc. To test this prediction, we have conducted a search for erupting dwarf novae in the center of 47 Tuc with 12 separate epochs of Hubble Space Telescope (HST ) images in visual through near-UV bands. We have found a second eruption of the dwarf nova V2 discovered by Paresce and De Marchi. In addition, we have discovered a faint blue variable with period D4.7 hr and amplitude 1.5 mag, which may be a cataclysmic variable. Detailed simulations demonstrate that our areal and tempo- ral coverage and detection sensitivity is sufficient to have detected one-third of all dwarf novae (via their eruptions) in the center of 47 Tuc; even the very faint U GemEtype objects. We therefore claim that there are probably no more than three dwarf novae in the core of 47 Tuc, in signi-cant disagreement with a key prediction of the standard model of tidal capture, unless the properties of dwarf novae in globulars di†er (e.g., in outburst frequency) from those in the -eld. In addition, the cluster color- magnitude diagram reveals zero novalike variable candidates. Subject headings: globular clusters: individual (47 Tucanae) E novae, cataclysmic variables E stars: statistics

A Deep Survey for Galactic Wolf-Rayet Stars. II. Implications for Galactic Structure and Massive Star Formation*

We have completed a direct narrowband-broadband Schmidt plate survey of large areas of the southern Milky Way for new Wolf-Rayet (W-R) stars as faint as 19th b magnitude. The 31 newly detected stars in the completed survey are among the reddest and/or most distant known in the Galaxy. We have obtained spectra of all candidate W-R stars in the 22 fields stretching from l = 282° to l = 341° in longitude and Δb = 35 in latitude, covering about 180 square degrees. We also observed two isolated Milky Way fields centered at l = 0° and l = 8°. Eighteen new W-R stars are reported here for the first time. Combined with the 13 new W-R stars we have already reported in Carina, our list of 31 new Galactic W-R stars reaches 3–4 mag fainter than previous surveys. Thirteen of our 18 new W-R stars reported here are of subtype WN, while five are of subtype WC. We present and describe their spectra and subtypes, derive their distances, and discuss the significance of their locations along with all other W-R stars in the Galaxy. Our new W-R stars clearly demonstrate an increasing number ratio of WN to WC stars with increasing Galactocentric distance. We conclude with predictions of the total number of Galactic W-R stars that should be discovered in future IR surveys.

WFPC2 Observations of Star Clusters in the Magellanic Clouds. I. The Large Magellanic Cloud Globular Cluster Hodge 11

We present our analysis of Hubble Space Telescope Wide Field Planetary Camera 2 observations in F555W (broadband V ) and F450W (broadband B) of the globular cluster Hodge 11 in the Large Magellanic Cloud galaxy. The resulting V vs. B − V color-magnitude diagram reaches 2.4 mag below the main-sequence turnoff (which is at VTO = 22.65 ±0.10 mag or M TO V = 4.00 ±0.16 mag). Comparing the fiducial sequence of Hodge 11 with that of the Galactic globular cluster M92, we conclude that, within the accuracy of our photometry, the age of Hodge 11 is identical to that of M92 with a relative age-difference uncertainty ranging from 10% to 21%. Provided that Hodge 11 has always been a part of the Large Magellanic Cloud and was not stripped from the halo of the Milky Way or absorbed from a cannibalized dwarf spheroidal galaxy, then the oldest stars in the Large Magellanic Clouds and the Milky Way appear to have the same age.

The Ionizing Star Clusters of Giant H II Regions in NGC 2403

We present the results of a study on the massive star population down to about MV ~ -3.1, or 12–15 M⊙, of the most luminous giant H II regions in the nearby spiral galaxy NGC 2403, based on Hubble Space Telescope images and ground-based spectrograms. Particular emphasis is placed on the distribution of the Wolf-Rayet and red supergiant stars and the information they provide about the recent star-forming history of these large complexes. We find direct evidence for the presence of Wolf-Rayet (WR) stars in five of the six giant H II regions investigated; 25–40 WR stars are inferred for the sole NGC 2403-I giant H II region. Red supergiant (RSG) stars are mainly distributed over a more extended halo, while the young blue stars and most WR stars are in or close to a compact core. One appears to be seeing young cores of O and WR stars surrounded by older halos containing red supergiants. We propose a scenario in which RSG stars belonging to an early phase of star formation were followed by a more recent burst corresponding to a very blue mean sequence. Delayed trigger with preheating over several 100 pc by the first generation of massive stars allowed the build-up of the required confinement for the production of parsec-scale cluster cores with luminosity up to a few times 106 L⊙. Finally, we present some interesting objects found in the field of NGC 2403 outside the giant H II regions, such as field WR stars, globular clusters and background galaxies.

Unraveling the oldest and faintest recovered nova: CK Vulpeculae (1670)

A narrow-band H..cap alpha..+(N II) CCD image of the field of Nova CK Vul (1670) shows nebulosity with a morphology (suggestive of equatorial ejection) with several bright subcondensations, and a central star. The net H..cap alpha.. image also reveals a faint jet leading to an H..cap alpha..-bright knot, suggestive of polar ejection. Spectra of the equatorial and polar ejecta are similar to each other and to spectra of the shell of the recurrent nova T Pyx, but with lower excitation. Nitrogen appears enhanced, and the nebular density is low enough that its recombination time scale equals or exceeds the time since outburst. The reconstructed light curve of CK Vul shows it to have been a very slow nova, with large oscillations near maximum. Constraints on its distance place it at 550 +- 150 pc from the Sun, near the far side of, or perhaps within, an intervening obscuring cloud. The implied nebular expansion velocity is extraordinarily low, v/sub exp/ = 59 +- 16 km s/sup -1/, and may not represent the true extent of the ejecta. The present absolute magnitude of the central star, M/sub R/ = +10.4, is 6 mag fainter than canonical old novae, and requires a verymorexa0» low-mass secondary star (Sp.> or approx. = M3 V), short orbital period ( P< or approx. =3--6), and negligible mass transfer rate (m< or approx. =10/sup -11.5/ M/sub sun/ yr/sup -1/). If CK Vul represents a typical state for novae between outbursts, then published survey-based values of the space density and lifetimes of cataclysmic binaries may be seriously underestimated.«xa0less

Binary star orbits from speckle interferometry. 5: A combined speckle/spectroscopic study of the O star binary 15 Monocerotis

We report on the discovery of a speckle binary companion to the O7 V (f) star 15 Monocerotis. A study of published radial velocities in conjunction with new measurements from Kitt Peak National Observatory (KPNO) and IUE suggests that the star is also a spectroscopic binary with a period of 25 years and a large eccentricity. Thus, 15 Mon is the first O star to bridge the gap between the spectroscopic and visual separation regimes. We have used the stars membership in the cluster NGC 2264 together with the cluster distance to derive masses of 34 and 19 solar mass for the primary and secondary, respectively. Several of the He I line profiles display a broad shallow component which we associate with the secondary, and we estimate the secondarys classification to be O9.5 Vn. The new orbit leads to several important predictions that can be tested over the next few years.