PHOTOMETRY OF TWO POORLY STUDIED PLANETARY NEBULAE WITH BINARY CENTRAL STARS

ABSTRACT We have observed the central stars of two planetary nebulae, Abell 65 and Hubble 12, both of which are claimed to be close binary systems. We looked at the differential photometry from these systems in hopes of confirming previous reports of variability caused by close binaries. Binary interaction in a planetary nebula is a possible source of the structure of bi-polar or butterfly PN. We determined that one of the two systems, Abell 65, most likely exhibits variability due to irradiation of a cool companion or deformation of one companion caused by it filing a significant fraction of its Roche Lobe. We cannot confirm the binary classification until a complete light curve is obtained. With Hubble 12, which was claimed to be an eclipsing binary system with an irradiation effect, we found no clear variability indicative of a binary system and recommend that it be removed from the list of known binary central stars

Variability in Protoplanetary Nebulae: X. Multi-year Periods as an Indicator of Potential Binaries

New observations are presented of four evolved objects that display long, multi-year variations in their light curves. These are interpreted as good evidence of their binary nature, with the modulation caused by the barycenter motion of the evolved star resulting in a periodic obscuration by a circumbinary disk. Although protoplanetary nebulae (PPNe) commonly possess bipolar nebulae, which are thought to be shaped by a binary companion, there are very few PPNe in which a binary companion has been found. Three of the objects in this study appear to be PPNe, IRAS 07253-2001, 08005-2356, and 17542-0603, with long periods of 5.2, 6.9, and 8.2 yrs, respectively. The binary nature of IRAS 08005-2356 has recently been confirmed by a radial velocity study. Two samples, one of PPNe and the other of post-AGB star candidates, are investigated for further evidence on how common is a long-period light curve variation. Both samples suggest such light variations are not common. The fourth object, IRAS 20056+1834 (QY Sge), is an obscured RV Tau variable of the RVb subclass, with a long period of 3.9 yrs and pulsation periods of 102.9 and 51.5 days. The period of this object is seen to vary by 2%. Evidence is presented for a recent mass ejection in IRAS 17542-0603.Comment: 22 pages, 6 figures, 1 machine-readable tabl

Binary Central Stars of Planetary Nebulae Discovered Through Photometric Variability III: The Central Star of Abell 65

A growing number of close binary stars are being discovered among central stars of planetary nebulae. Recent and ongoing surveys are finding new systems and contributing to our knowledge of the evolution of close binary systems. The push to find more systems was largely based on early discoveries which suggested that 10 to 15% of all central stars are close binaries. One goal of this series of papers is confirmation and classification of these systems as close binaries and determination of binary system parameters. Here we provide time-resolved multi-wavelength photometry of the central star of Abell 65 as well as further analysis of the nebula and discussion of possible binary--nebula connections. Our results for Abell 65 confirm recent work showing that it has a close, cool binary companion, though several of our model parameters disagree with the recently published values. With our longer time baseline of photometric observations from 1989--2009 we also provide a more precise orbital period of 1.0037577 days.Comment: Accepted for publication in the Astronomical Journa

The Remote Observatories of the Southeastern Association for Research in Astronomy (SARA)

We describe the remote facilities operated by the Southeastern Association for Research in Astronomy (SARA) , a consortium of colleges and universities in the US partnered with Lowell Observatory, the Chilean National Telescope Allocation Committee, and the Instituto de Astrofísica de Canarias. SARA observatories comprise a 0.96 m telescope at Kitt Peak, Arizona; one of 0.6 m aperture on Cerro Tololo, Chile; and the 1 m Jacobus Kapteyn Telescope at the Roque de los Muchachos, La Palma, Spain. All are operated using standard VNC or Radmin protocols communicating with on-site PCs. Remote operation offers considerable flexibility in scheduling, allowing long-term observational cadences difficult to achieve with classical observing at remote facilities, as well as obvious travel savings. Multiple observers at different locations can share a telescope for training, educational use, or collaborative research programs. Each telescope has a CCD system for optical imaging, using thermoelectric cooling to avoid the need for frequent local service, and a second CCD for offset guiding. The Arizona and Chile telescopes also have fiber-fed echelle spectrographs. Switching between imaging and spectroscopy is very rapid, so a night can easily accommodate mixed observing modes. We present some sample observational programs. For the benefit of other groups organizing similar consortia, we describe the operating structure and principles of SARA, as well as some lessons learned from almost 20 years of remote operations

Modeling the SS 433 Jet Bends

We fit Chandra HETGS data obtained for the unusual X-ray binary SS 433. While line strengths and continuum levels hardly change, the jet Doppler shifts show aperiodic variations that probably result from shocks in interactions with the local environment. The X-ray and optical emission line regions are found to be related but not coincident as the optical line emission persists for days while the X-ray emission lines fade in less than 5000 s. The X-ray spectrum of the blue-shifted jet shows over two dozen emission lines from plasma at a variety of temperatures. The emission measure distribution derived from the spectrum can be used to test jet cooling models.Comment: 4 pages, 3 figure, presented at the conference on "Hign Energy Phenomena in Relativistic Outflows", Dublin, September 200

Variability in Proto-Planetary Nebulae: VI. Multi-Telescope Light Curves Studies of Several Medium-Bright (V=13-15), Carbon-Rich Objects

We present ten years of new photometric monitoring of the light variability of five evolved stars with strong mid-infrared emission from surrounding dust. Three are known carbon-rich proto-planetary nebulae (PPNe) with F$-$G spectral types; the nature of the other two was previously unknown. For the three PPNe, we determine or refine the pulsation periods of IRAS 04296+3429 (71 days), 06530$-$0213 (80 days), and 23304+6147 (84 days). A secondary period was found for each, with a period ratio P$_2$/P$_1$ of 0.9. The light variations are small, 0.1-0.2 mag. These are similar to values found in other PPNe. The other two are found to be giant stars. IRAS 09296+1159 pulsates with a period of only 47 days but reaches pulsational light variations of 0.5 mag. Supplemental spectroscopy reveals the spectrum of a CH carbon star. IRAS 08359$-$1644 is a G1III star that does not display pulsational variability; rather, it shows non-periodic decreases of brightness of up to 0.5 mag over this ten-year interval. These drops in brightness are reminiscent of the light curves of R Corona Borealis variables, but with much smaller decreases in brightness, and are likely due to transient dust obscuration. Its SED is very similar to that of the unusual oxygen-rich giant star HDE 233517, which possesses mid-infrared hydrocarbon emission features. These two non-PPNe turn out to members of the rare group of giant stars with large mid-infrared excesses due to dust, objects which presumably have interesting evolutionary histories.Comment: 25 pages, 14 figures, 1 electronic table, accepted for publication in the Astronomical Journa