Discovery of an Unusual High State in the Long-Term Light Curve of AM Herculis

The magnetic cataclysmic variable archetype AM Herculis is known to display high and low photometric states, in which it switches from Roche lobe-overflow accretion (high) to wind accretion (low). The origin of this behavior is still unknown (although it is believed to be linked to the presence of starspots located near the L1 point on the secondary star), as are the specifics of duration and frequency of the two states. During the recent (2007) transition from an exceptionally long period of persistent low state behavior back to the high state, AM Her entered a short (~2 month) intermediate state, in which its brightness remained at ~0.5 mag fainter than the normal high-state level. Within the recorded history of AM Her, this was the first time the system displayed such behavior. Using data from the American Association of Variable Star Observers, we compare the characteristics of this faint high state to the subsequent normal high state, and a prior "failed high state," in which the system briefly reached a brightness level near that of the normal high state before rapidly returning to the low state. The distribution of magnitude values attained during each state, along with the shapes of the orbital light curve in each state, support a scenario in which the specific configuration of the accretion flow between the secondary star and the white dwarf must be rapidly established at the end of a low state, even before the mass transfer rate has reached the normal high-state level

White Dwarf - Red Dwarf Systems Resolved with the Hubble Space Telescope. II. Full Snapshot Survey Results

Results are presented for a Hubble Space Telescope Advanced Camera for Surveys high-resolution imaging campaign of 90 white dwarfs with known or suspected low mass stellar and substellar companions. Of the 72 targets which remain candidate and confirmed white dwarfs with near-infrared excess, 43 are spatially resolved into two or more components, and a total of 12 systems are potentially triples. There is a possible, slight deficit of earlier spectral types (bluer colors) among the spatially unresolved companions, exactly the opposite of expectations if significant mass is transferred to the companion during the common envelope phase. Using the best available distance estimates, the low mass companions to white dwarfs exhibit a bimodal distribution in projected separation. This result supports the hypothesis that during the giant phases of the white dwarf progenitor, any unevolved companions either migrate inward to short periods of hours to days, or outward to periods of hundreds to thousands of years. No intermediate projected separations of a few to several AU are found among these pairs. However, a few double M dwarfs (within triples) are spatially resolved in this range, empirically demonstrating that such separations were readily detectable among the binaries with white dwarfs. A straightforward and testable prediction emerges: all spatially unresolved, low mass stellar and substellar companions to white dwarfs should be in short period orbits. This result has implications for substellar companion and planetary orbital evolution during the post-main sequence lifetime of their stellar hosts.Comment: Accepted to ApJ Supplement Series, emulateapj format, 14 figures, 8 table

Recent Results from Infrared Observations of White Dwarfs, their Companions, and the Dust that Surrounds Them

Although "traditionally" observed at short wavelengths, white dwarfs have displayed many surprising features when probed in the infrared. We present an overview of recent results from ground- and space-based near- to mid-infrared observations of white dwarfs. These include the discovery of many new candidate binary stars containing low mass stellar or sub-stellar companions from a sample of objects previously thought to be single white dwarfs, and Spitzer Space Telescope observations that suggest that dust is common in the environs of white dwarfs in cataclysmic variables

Mid-Infrared Circumstellar Shell Sources Discovered with Spitzer: An Obscured Population of Massive Stars?

We have discovered a large number of circular and elliptical shells around luminous central sources at 24 μm with the MIPS instrument on board the Spitzer Space Telescope. Most of these shells are not visible in the shorter wavelengths bands of IRAC or archival 2MASS and optical images. On the other hand, many of the central stars are detected in the 2MASS catalog, but lack an optical counterpart, indicating that we are dealing with a population of highly obscured objects. Our archival follow-up effort has revealed 90% of these shell sources to be previously unknown

A New Narrow-Line Seyfert 1 galaxy : RXJ1236.9+2656

We report identification of a narrow-line Seyfert 1 galaxy RXJ1236.9+2656. X-ray emission from the NLS1 galaxy undergoes long-term variability with 0.1--2.0 keV flux changing by a factor of 2 within about 3 yr. The ROSAT PSPC spectrum of RXJ1236.9+2656 is well represented by a power-law of Gamma = 3.7 absorbed by matter in our own Galaxy (N_H = 1.33X10^20 cm**-2). Intrinsic soft X-ray luminosity of the NLS1 galaxy is estimated to be 1.5X10^43 erg/s in the energy band of 0.1-2.0 keV. The optical spectrum of RXJ1236.9+2656 is typical of NLS1 galaxies and shows narrow Balmer emission lines (1100 km/s < FWHM < 1700 km/s) of Hbeta, Halpha, and forbidden lines of [O III] and [N II]. Fe II multiplets, usually present in optical spectra of NLS1 galaxies, are also detected in RXJ1236.9+2656.Comment: 4 pages, A&A style Latex, To apear in A&A as a research not

The WISE InfraRed Excesses around Degenerates (WIRED) Survey

The Wide-field Infrared Survey Explorer (WISE) is a NASA medium class Explorer mission that performed an all sky survey in four infrared bands. We present an overview of the WISE InfraRed Excesses around Degenerates (WIRED) Survey, which has the goals of characterizing white dwarf stars in the WISE bands, confirming objects known to have infrared excess from past observations, and revealing new examples of white dwarfs with infrared excess that can be attributed to unresolved companions or debris disks. We obtained preliminary WISE detections (S/N > 2) in at least one band of 405 white dwarfs from the 9316 unique possible targets in the Sloan Digital Sky Survey Data Release 4 Catalog of Spectroscopically Identified White Dwarfs (not all potential targets were available in the sky coverage used here). A companion paper in this volume discusses specific results from our target detections

Near-infrared Observations of the Proto-Planetary Nebula IRAS~07131-0147

We have obtained near-infrared imaging and an optical spectrum of the proto-planetary nebula IRAS~07131-0147, a highly polarized bipolar reflection nebula believed to be in evolutionary transition from the asymptotic giant branch to the planetary nebula phase. Our images reveal point reflection symmetry in the lobes - a relatively rare morphological feature. We place an upper limit on the distance of 6.5 kpc. Utilizing numerical integrations of single grain scattering models we find the nebula to lie at an inclination angle of i=20\pm5 degrees in the plane of the sky. We present a refined geometric interpretation of IRAS~07131-0147 consistent with our new observational data and argue that the central star is likely to have an as yet undetected binary companion.Comment: 16 pages, compressed uuencoded file includes 6 postscript figures, also available via anonymous ftp at ftp://igpp.llnl.gov/pub/alves/; accepted for publication in the Astronomical Journa