J. R. Kuhn

Imaging polarimetric observations of a new circumstellar disk system

Few circumstellar disks have been observed directly. Here we use sensitive differential polarimetric techniques to overcome atmospheric speckle noise in order to image the circumstellar material around HD 169142. The detected envelope or disk is considerably smaller than expectations based on the measured strength of the far-IR excess from this system.

THE SOLAR-SYSTEM-SCALE DISK AROUND AB AURIGAE

The young star AB Aurigae is surrounded by a complex combination of gas-rich and dust-dominated structures. The inner disk, which has not been studied previously at sufficient resolution and imaging dynamic range, seems to contain very little gas inside a radius of least 130 AU from the star. Using adaptive optics coronagraphy and polarimetry, we have imaged the dust in an annulus between 43 and 302 AU from the star, a region never seen before. An azimuthal gap in an annulus of dust at a radius of 102 AU, along with a clearing at closer radii inside this annulus, suggests the formation of at least one small body at an orbital distance of ~100 AU. This structure seems consistent with crude models of mean motion resonances or accumulation of material at two of the Lagrange points relative to the putative object and the star. We also report a low significance detection of a point source in this outer annulus of dust. This source may be an overdensity in the disk due to dust accreting onto an unseen companion. An alternate interpretation suggests that the objects mass is between 5 and 37 times the mass of Jupiter. The results have implications for circumstellar disk dynamics and planet formation.

Earth-Based Observations of the Galileo Probe Entry Site

Earth-based observations of Jupiter indicate that the Galileo probe probably entered Jupiters atmosphere just inside a region that has less cloud cover and drier conditions than more than 99 percent of the rest of the planet. The visual appearance of the clouds at the site was generally dark at longer wavelengths. The tropospheric and stratospheric temperature fields have a strong longitudinal wave structure that is expected to manifest itself in the vertical temperature profile.

THE LYOT PROJECT DIRECT IMAGING SURVEY OF SUBSTELLAR COMPANIONS: STATISTICAL ANALYSIS AND INFORMATION FROM NONDETECTIONS

The Lyot project used an optimized Lyot coronagraph with extreme adaptive optics at the 3.63 m Advanced Electro-Optical System telescope to observe 86 stars from 2004 to 2007. In this paper, we give an overview of the survey results and a statistical analysis of the observed nondetections around 58 of our targets to place constraints on the population of substellar companions to nearby stars. The observations did not detect any companion in the substellar regime. Since null results can be as important as detections, we analyzed each observation to determine the characteristics of the companions that can be ruled out. For this purpose, we use a Monte Carlo approach to produce artificial companions and determine their detectability by comparison with the sensitivity curve for each star. All the non-detection results are combined using a Bayesian approach and we provide upper limits on the population of giant exoplanets and brown dwarfs for this sample of stars. Our nondetections confirm the rarity of brown dwarfs around solar-like stars and we constrain the frequency of massive substellar companions (M>40 M_J) at orbital separation between and 10 and 50 AU to be ≲20%.

Spectropolarimetric Observations of Herbig Ae/Be Stars. II. Comparison of Spectropolarimetric Surveys: Haebe, Be and Other Emission-Line Stars

The polarization of light across individual spectral lines contains information about the circumstellar environment on very small spatial scales. We have obtained a large number of high-precision, high-resolution spectropolarimetric observations of Herbig Ae/Be, Classical Be and other emission-line stars collected on 117 nights of observations with the Hi-Resolution Visible spectropolarimeter at a resolution of R = 13, 000 on the 3.67 m Advanced Electro-Optical System telescope. We also have many observations from the ESPaDOnS spectropolarimeter at a resolution of R = 68, 000 on the 3.6 m Canada-France-Hawaii Telescope. In roughly ~2/3 of the so-called windy or disky Herbig Ae/Be stars, the detected Hα linear polarization varies from our typical detection threshold near 0.1% to over 2%. In all but one HAe/Be star, the detected polarization effect is not coincident with the Hα emission peak but is detected in and around the obvious absorptive part of the line profile. The qu-loops are dominated by the polarization in this absorptive region. In several stars, the polarization varies in time mostly in the absorptive component and is not necessarily tied to corresponding variations in intensity. This is a new result not seen at lower resolution. In the Be and emission-line stars, ten out of a sample of 30 show a typical broad depolarization effect but four of these ten show weaker effects only visible at high resolution. Another five of 30 show smaller amplitude, more complex signatures. Six stars of alternate classification showed large amplitude (1%-3%) absorptive polarization effects. These detections are largely inconsistent with the traditional disk-scattering and depolarization models.

Line-profile Variability from Tidal Flows in Alpha Virginis (Spica)

We present the results of high precision, high resolution (R~68000) optical observations of the short-period (4d) eccentric binary system Alpha Virginis (Spica) showing the photospheric line-profile variability that in this system can be attributed to non-radial pulsations driven by tidal effects. Although scant in orbital phase coverage, the data provide S/N>2000 line profiles at full spectral resolution in the wavelength range delta-lambda = 4000--8500 Angstroms, allowing a detailed study of the night-to-night variability as well as changes that occur on ~2 hr timescale. Using an ab initio theoretical calculation, we show that the line-profile variability can arise as a natural consequence of surface flows that are induced by the tidal interaction.

A New Mechanism for Polarizing Light from Obscured Stars

Recent spectropolarimetric observations of Herbig Ae/Be stellar systems show linear polarization variability with wavelength and epoch near their obscured Ha emission. Surprisingly, this polarization is not coincident with the Ha emission peak but is variable near the absorptive part of the line profile. With a new and novel model, we show here that this is evidence of optical pumping—anisotropy of the incident radiation that leads to a linear polarization-dependent optical depth within the intervening hydrogen wind or disk cloud. This effect can yield a larger polarization signal than scattering polarization in these systems.

Spectropolarimetry of the Deep Impact target Comet 9P/Tempel 1 with HiVIS ☆

Spectropolarimetry of the Deep Impact target, comet 9P/ Tempel 1, was performed during the impact event on July 4th, 2005 with the HiVIS Spectropolarimeter and the AEOS 3.67m telescope on Haleakala, Maui. We observed atypical polarization spectra that changed significantly in the few hours after the impact. The polarization is sensitive to the geometry, size and composition of the scattering particles. Our first measurement, beginning 8 minutes after impact and centered at 6:30UT, showed a polarization of 4% at 650 nm falling to 3% at 950 nm. The next observation, centered an hour later, showed a polarization of 7% at 650 nm falling to 2% at 950nm. This corresponds to a spectropolarimetric gradient, or slope, of -0.9% per 1000Å 40 minutes after impact, decreasing to a slope of -2.3% per 1000Å 75 minutes after impact. Both are atypical blue polarization slopes. The polarization values of 4% and 7% at 650nm are typical for comets at this scattering angle, whereas the low polarization of 2% and 3% at 950nm is not. This, combined with the IR spectroscopy performed by a number of observers during the event, suggests an increase in size, number, and crystallinity of the individual silicate particles (monomers) that are a constituant of the dust particles (aggregates) in the ejecta.