We have carried out a multiwavelength observational campaign demonstrating some of the remarkable properties of the infrared-bright variable star BP Psc. Surrounded by a compact dusty, gaseous disk, this little-studied late G ( or early K) type star emits about 75% of its detected energy flux at infrared wavelengths. Evidence for accretion of gas in conjunction with narrow bipolar jets and Herbig-Haro objects is apparently consistent with classification of BP Psc as a pre-main-sequence star, as postulated in most previous studies. If young, then BP Psc would be one of the nearest and oldest known classical T Tauri stars. However, such an evolutionary classification encounters various problems that are absent or much less severe if BP Psc is instead a luminosity class III post-main-sequence star. In this case, it would be the first known example of a first-ascent giant surrounded by a massive molecular disk with accompanying rapid gas accretion and prominent jets and HH objects. In this model, the genesis of the massive dusty gaseous disk could be a consequence of the envelopment of a low-mass companion star. Properties in the disk may be conducive to the current formation of planets, a gigayear or more after the formation of BP Psc itself.

We report HST NICMOS coronagraphic images of the HD 15115 circumstellar disk at 1.1 mm. We find a similar morphology to that seen in the visible and at H band-an edge-on disk that is asymmetric in surface brightness. Several aspects of the 1.1 mu m data are different, highlighting the need for multiwavelength images of each circumstellar disk. We find a flattening to the western surface brightness profile at 1.1 mu m interior to 2 '' ( 90 AU) and a warp in the western half of the disk. We measure the surface brightness profiles of the two disk lobes and create a measure of the dust scattering efficiency between 0.55 and 1.65 mu m at 1 '', 2 '', and 3 ''. At 2 '' the western lobe has a neutral spectrum up to 1.1 mu m and a strong absorption or blue spectrum 11.1 mu m, while a blue trend is seen in the eastern lobe. At 1 '' the disk has a red color in both lobes.

We present the results of a search for a young stellar moving group associated with the star HD 141569 - a nearby, isolated Herbig AeBe primary member of a 5 +/- 3 Myr-old triple star system on the outskirts of the Sco-Cen complex. Our spectroscopic survey identified a population of 21 Li-rich, less than or similar to 30 Myr-old stars within 30 degrees of HD 141569 which possess similar proper motions with the star. The spatial distribution of these Li-rich stars, however, is not suggestive of a moving group associated with the HD 141569 triplet, but rather this sample appears cospatial with Upper Scorpius (US) and Upper Centaurus Lupus (UCL). We apply a modified moving cluster parallax method to compare the kinematics of these youthful stars with those of the US and UCL. Eight new potential members of US and five new potential members of UCL are identified. A substantial moving group with an identifiable nucleus within 15 degrees (similar to 30 pc) of HD 141569 is not found in this sample. Evidently, the HD 141569 system formed similar to 5 Myr ago in relative isolation, tens of parsecs away from the recent sites of star formation in the Ophiucus-Scorpius-Centaurus region.

We have obtained high spatial resolution imaging observations of the HR 4796A circumstellar debris dust ring using the broad optical response of the Hubble Space Telescope Imaging Spectrograph (STIS) in coronagraphic mode. We use our visual wavelength observations to improve upon the earlier measured geometrical parameters of the ring-like disk. Two significant flux density asymmetries are noted: (1) preferential forward scattering by the disk grains and (2) an azimuthal surface brightness anisotropy about the morphological minor axis of the disk with corresponding differential ansal brightness. We find the debris ring offset from the location of the star by similar to 1.4 AU, a shift insufficient to explain the differing brightnesses of the northeast and southwest ansae simply by the 1/r(2) dimmunition of starlight. The STIS data also better quantify the radial confinement of the starlight-scattering circumstellar debris, to a characteristic region less than 14 AU in photometric half-width, with a significantly steeper inner truncation than outward falloff in radial surface brightness. The inferred spatial distribution of the disk grains is consistent with the possibility of one or more unseen co-orbital planetary-mass perturbers, and the colors of the disk grains are consistent with a collisionally evolved population of debris, possibly including ices reddened by radiation exposure to the central star.

We detect the HD 32297 debris disk in scattered light at 1.6 and 2.05 mu m. We use these new observations together with a previous scattered light image of the disk at 1.1 mu m to examine the structure and scattering efficiency of the disk as a function of wavelength. In addition to surface brightness asymmetries and a warped morphology beyond similar to 1 ''.5 for one lobe of the disk, we find that there exists an asymmetry in the spectral features of the grains between the northeastern and southwestern lobes. The mostly neutral color of the disk lobes implies roughly 1 mu m-sized grains are responsible for the scattering. We find that the asymmetries in color and morphology can plausibly be explained by HD 32297's motion into a dense interstellar medium cloud at a relative velocity of 15 km s(-1). We model the interaction of dust grains with H I gas in the cloud. We argue that supersonic ballistic drag can explain the morphology of the debris disks of HD 32297, HD 15115, and HD 61005.

We present high-resolution (R = 55,000) optical spectra obtained with MIKE on the 6.5 m Magellan Clay Telescope as well as Spitzer MIPS photometry and Infrared Spectrometer low-resolution (R similar to 60) spectroscopy of the close (14 AU separation) binary, HD 101088, a member of the similar to 12 Myr old southern region of the Lower Centaurus Crux subgroup of the Scorpius-Centaurus OB association. We find that the primary and/or secondary is accreting from a tenuous circumprimary and/or circumsecondary disk despite the apparent lack of a massive circumbinary disk. We estimate a lower limit to the accretion rate of M > 1 x 10(-9) M-circle dot yr(-1), which our multiple observation epochs show varies over a timescale of months. The upper limit on the 70 mu m flux allows us to place an upper limit on the mass of dust grains smaller than several microns present in a circumbinary disk of 0.16 M-moon. We conclude that the classification of disks into either protoplanetary or debris disks based on fractional infrared luminosity alone may be misleading.

Spitzer Space Telescope photometry and spectroscopy of BD+20 307 show that all of the dust around this remarkable Gyr-old spectroscopic binary arises within 1 AU. No additional cold dust is needed to fit the infrared excess. Peaks in the 10 and 20 mu m spectrum are well fit with small silicates that should be removed on a timescale of years from the system. This is the dustiest star known for its age, which is greater than or similar to 1 Gyr. The dust cannot arise from a steady-state collisional cascade. A catastrophic collision of two rocky, planetary-scale bodies in the terrestrial zone is the most likely source for this warm dust because it does not require a reservoir of planetesimals in the outer system.

The census of young moving groups in the solar neighborhood is significantly incomplete in the low-mass regime. We have developed a new selection process to find these missing members based on the Galaxy Evolution Explorer (GALEX) All-Sky Imaging Survey (AIS). For stars with spectral types greater than or similar to K5 (R - J greater than or similar to 1.5) and younger than approximate to 300 Myr, we show that near-UV (NUV) and far-UV (FUV) emission is greatly enhanced above the quiescent photosphere, analogous to the enhanced X-ray emission of young low-mass stars seen by ROSAT but detectable to much larger distances with GALEX. By combining GALEX data with optical (HST Guide Star Catalog) and near-IR (2MASS) photometry, we identified an initial sample of 34 young M dwarf candidates in a 1000 deg(2) region around the approximate to 10 Myr TW Hydra Association (TWA). Low-resolution spectroscopy of 30 of these found 16 which had Ha in emission, which were then followed up at high resolution to search for spectroscopic evidence of youth and to measure their radial velocities. Four objects have low surface gravities, photometric distances and space motions consistent with TWA, but the non-detection of Li indicates that they may be too old to belong to this moving group. One object (M3.5, 93 +/- 19 pc) appears to be the first known accreting low-mass member of the approximate to 15 Myr Lower Centaurus Crux OB association. Two objects exhibit all the characteristics of the known TWA members, and thus we designate them as TWA 31 (M4.2, 110 +/- 11 pc) and TWA 32 (M6.3, 53 +/- 5 pc). TWA 31 shows extremely broad (447 km s(-1)) H alpha emission, making it the sixth member of TWA found to have ongoing accretion. TWA 32 is resolved into a 0 ''.6 binary in Keck laser guide star adaptive optics imaging. Our search should be sensitive down to spectral types of at least M4-M5 in TWA and thus the small numbers of new member is puzzling. This might indicate TWA has an atypical mass function or that the presence of lithium absorption may be too restrictive a criteria for selecting young low-mass stars.

We obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 mu m and 70 mu m observations of 182 nearby, Hipparcos F-and G-type common proper motion single and binary systems in the nearest OB association, Scorpius-Centaurus. We also obtained Magellan/MIKE R similar to 50,000 visual spectra at 3500-10500 angstrom for 181 candidate ScoCen stars in single and binary systems. Combining our MIPS observations with those of other ScoCen stars in the literature, we estimate 24 mu mF+G-type disk fractions of 9/27 (33% +/- 11%), 21/67 (31% +/- 7%), and 25/71 (35% +/- 7%) for Upper Scorpius (similar to 10 Myr), Upper Centaurus Lupus (similar to 15 Myr), and Lower Centaurus Crux (similar to 17 Myr), respectively. We confirm previous IRAS and MIPS excess detections and present new discoveries of 41 protoplanetary and debris disk systems, with fractional infrared luminosities ranging from L-IR/L-* = 10(-5) to 10(-2) and grain temperatures ranging from T-gr = 40-300 K. We searched for an increase in 24 mu m excess at an age of 15-20 Myr, consistent with the onset of debris production predicted by coagulation N-body simulations of outer planetary systems. We found such an increase around 1.5M(circle dot) stars but discovered a decrease in the 24 mu m excess around 1.0 M-circle dot stars. We additionally discovered that the 24 mu m excess around 1.0 M-circle dot stars is larger than predicted by self-stirred models. Finally, we found a weak anti-correlation between fractional infrared luminosity (L-IR/L-*) and chromospheric activity (R'(HK)), that may be the result of differences in stellar properties, such as mass, luminosity, and/or winds.