Bibcode
Pereyra, A.; Girart, J. M.; Magalhães, A. M.; Rodrigues, C. V.; de Araújo, F. X.
Bibliographical reference
Astronomy and Astrophysics, Volume 501, Issue 2, 2009, pp.595-607
Advertised on:
7
2009
Journal
Citations
19
Refereed citations
18
Description
Aims: Our goal is to study the physical properties of the circumstellar
environment of young stellar objetcs (YSOs). In particular, the
determination of the scattering mechanism can help us to constrain the
optical depth of the disk and/or envelope in the near infrared. Methods: We used the IAGPOL imaging polarimeter along with the CamIV
infrared camera at the LNA observatory to obtain near infrared
polarimetry measurements in the H band of a sample of optically visible
YSOs, namely, eleven T Tauri stars and eight Herbig Ae/Be stars. An
independent determination of the disk (or jet) orientation was obtained
for twelve objects from the literature. The circumstellar optical depth
could then be estimated by comparing the integrated polarization
position angle (PA) with the direction of the major axis of the disk
projected onto the plane of the sky. Optically thin disks have, in
general, a polarization PA that is perpendicular to the disk plane. In
contrast, optically thick disks have polarization PAs parallel to the
disks. Results: Among the T Tauri stars, three are consistent
with having optically thin disks (AS 353A,
RY Tau and UY Aur) and five with
optically thick disks (V536 Aql, DG
Tau, DO Tau, HL Tau and
LkHα 358). Among the Herbig Ae/Be stars, two
stars exhibit evidence of optically thin disks (Hen
3-1191 and VV Ser) and two of optically
thick disks (PDS 453 and MWC 297).
Our results seem consistent with optically thick disks at near infrared
bands, which are more likely to be associated with younger YSOs.
Marginal evidence of polarization reversal is found in RY
Tau, RY Ori, WW Vul, and
UY Aur. In the first three cases, this feature can be
associated with the UXOR phenomenon. Correlations with the IRAS colors
and the spectral index yielded evidence of an evolutionary segregation
in which the disks tend to be optically thin when they are older.
Based on observations obtained at the Observatório do Pico dos
Dias, LNA/MCT, Itajubá, Brazil.