Astrophys. J., 661, 944-971 (2007/June-1)
Spitzer limits on dust emission and optical gas absorption variability around nearby stars with edge-on circumstellar disk signatures.
REDFIELD S., KESSLER-SILACCI J.E. and CIEZA L.A.
Abstract (from CDS):
We present Spitzer infrared spectroscopic and photometric observations and McDonald Observatory Smith Telescope and AAT high spectral resolution optical observations of four nearby stars with variable or anomalous optical absorption, likely caused by circumstellar material. The optical observations of Ca II and Na I cover a 2.8 yr baseline and extend the long-term monitoring of these systems by previous researchers. In addition, minisurveys of the LISM around our primary targets provide a reconstruction of the intervening LISM along the line of sight. We confirm that the anomalous absorption detected toward α Oph is not due to circumstellar material, but to a small filamentary cloud <14.3 pc from the Sun. The three other primary targets, β Car, HD 85905, and HR 10, show both short- and long-term variability, and little of the observed absorption can be attributed to the LISM along the line of sight. The Spitzer photometry and spectroscopy did not detect infrared excesses. For the three disk stars, we fit the maximum hypothetical infrared excess that is consistent with observed upper limits. We place upper limits on any possible fractional infrared luminosity, LIR/L*<(2-5)x10–6. These fractional luminosities are significantly less than that found toward β Pic but comparable to other debris disks. No stable gas absorption component centered at the radial velocity of the star is detected, consistent with no infrared excess detections. Based on simple assumptions of the variable gas absorption component, we estimate limits on the circumstellar gas mass causing the variable absorption: (0.4-20)x10–8 M⊕. These multiwavelength observations place strong limits on any possible circumstellar dust, while confirming variable circumstellar gas absorption, and therefore are interesting targets to explore the origins and evolution of variable circumstellar gas.
Stars: Circumstellar Matter - Infrared: Stars - ISM: Structure - Line: Profiles - Stars: Early-Type - stars: individual (α Oph) - stars: individual (β Car) - stars: individual (HD 85905) - Stars: Individual: Bright Star Number: HR 10
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