arXiv subjects

F. Menard

Publications and source records attributed to F. Menard.

130 records · Page 8Linked to original sources

arXiv2000

HST/NICMOS2 coronagraphic observations of the circumstellar environment of three old PMS stars: HD 100546, SAO 206462 and MWC 480

The close environment of four old Pre-Main Sequence stars has been observed thanks to the coronagraphic mode of the HST/NICMOS2 camera at lambda=1.6 micron. In the course of this program, the detection of a circumstellar annulus around HD 141569 has already been presented in Augereau et al.(1999b). In this paper, we report the detection of an elliptical structure around the Herbig Be star HD 100546 extending from the very close edge of the coronagraphic mask (~50 AU) to 350-380 AU (3.5-3.8 arcsec) from the star. The axis ratio gives a disk inclination of 51+/-3 degrees to the line-of-sight and a position angle of 161+/-5 degrees, measured east of north. At 50 AU, the disk has a surface brightness between 10.5 and 11 mag/arcsec^2, then follows a -2.92+/-0.04 radial power law up to 250-270 AU and finally falls as r^{-5.5+/-0.2}. The inferred optical thickness suggests that the disk is at least marginally optically thick inside 80 AU and optically thin further out. Combined with anisotropic scattering properties, this could explain the shape of a brightness asymmetry observed along the minor axis of the disk. This asymmetry needs to be confirmed. The circumstellar disks around SAO 206462 and MWC 480 are not resolved, leading to constraints on the dust distribution. A tight binary system separated by only 0.32+/-0.04 arcsec is nevertheless detected in the close vicinity of SAO 206462.

astro-ph↗

arXiv2000

Circumbinary disks around T Tauri stars: HST/NICMOS near-infrared images and polarimetric maps

We have obtained new near-infrared images of both GG Tau and UY Aur circumbinary disks with the polarimetric modes of NICMOS aboard the Hubble Space Telescope. The 1 micron intensity map of GG Tau reveals a more complete elliptical shape than in previous ground-based images. Its eastern and western sides are definitely asymmetric. Our image strongly supports the ring geometry proposed by Guilloteau, Dutrey & Simon (1999) on the basis of their millimetre interferometry images: a geometrically thick and sharply edged ring surrounding an empty gap around the binary. Around UY Aur, we identify structures that are in excellent agreement with the optical images of Ménard et al. (1999), which confirms that the inclination of the system to the line-of-sight is about 60 degrees. We also find tentative new structures closer to the stars.

astro-ph↗

arXiv2000

Direct Observation of the Fourth Star in the Zeta Cancri System

Direct imaging of the zeta Cnc system has resolved the fourth star in the system, which is in orbit around zeta Cnc C. The presence of the fourth star has been inferred for many years from irregularities in the motion of star C, and recently from C's spectroscopic orbit. However, its mass is close to that of C, making its non-detection puzzling. Observing at wavelengths of 1.2, 1.7, and 2.2 microns with the adaptive-optics system of the CFHT, we have obtained images which very clearly reveal star D and show it to have the color of an M2 star. Its brightness is consonant with its being two M stars, which are not resolved in our observations but are likely to be in a short-period orbit, thereby accounting for the large mass and the difficulty of detection at optical wavelengths, where the magnitude difference is much larger. The positions and colors of all four stars in the system are reported and are consistent with the most recent astrometric observations.

astro-ph↗

arXiv1999

HST/NICMOS2 observations of the HD 141569 A circumstellar disk

We report the first resolved scattered light images of the circumstellar dust disk around the old Pre-Main Sequence star HD 141569 A. The disk seen in HST/NICMOS2 images shapes a bright annulus inclined at 37.5 degrees +/- 4.5 degrees from edge-on. This ring peaks at 325+/-10 AU from the star with a characteristic width of ~150 AU. At 1.6 microns, the dust grains scatter a total flux density of at least 4.5 +/- 0.5 mJy. Our disk model using the spatial distribution implied by the images does not explain the 10 microns excess and requires an additional grain population closer to the star. Some similarities and differences with the dust annulus surrounding HR 4796 A are pointed out.

astro-ph↗