6 research outputs found
Mid-infrared size survey of Young Stellar Objects: Description of Keck segment-tilting experiment and basic results
The mid-infrared properties of pre-planetary disks are sensitive to the
temperature and flaring profiles of disks for the regions where planet
formation is expected to occur. In order to constrain theories of planet
formation, we have carried out a mid-infrared (wavelength 10.7 microns) size
survey of young stellar objects using the segmented Keck telescope in a novel
configuration. We introduced a customized pattern of tilts to individual mirror
segments to allow efficient sparse-aperture interferometry, allowing full
aperture synthesis imaging with higher calibration precision than traditional
imaging. In contrast to previous surveys on smaller telescopes and with poorer
calibration precision, we find most objects in our sample are partially
resolved. Here we present the main observational results of our survey of 5
embedded massive protostars, 25 Herbig Ae/Be stars, 3 T Tauri stars, 1 FU Ori
system, and 5 emission-line objects of uncertain classification. The observed
mid-infrared sizes do not obey the size-luminosity relation found at
near-infrared wavelengths and a companion paper will provide further modelling
analysis of this sample. In addition, we report imaging results for a few of
the most resolved objects, including complex emission around embedded massive
protostars, the photoevaporating circumbinary disk around MWC 361A, and the
subarcsecond binaries T Tau, FU Ori and MWC 1080.Comment: Accepted by Astrophysical Journal. 38 pages. 9 figure
An Extragalactic 12CO J=3-2 survey with the Heinrich-Hertz-Telescope
We present results of a ^{12}CO J = 3-2 survey of 125 nearby galaxies
obtained with the 10-m Heinrich-Hertz-Telescope, with the aim to characterize
the properties of warm and dense molecular gas in a large variety of
environments. With an angular resolution of 22'', ^{12}CO 3-2 emission was
detected in 114 targets. Based on 61 galaxies observed with equal beam sizes
the ^{12}CO 3-2/1-0 integrated line intensity ratio R_{31} is found to vary
from 0.2 to 1.9, with an average value of 0.81. No correlations are found for
R_{31} to Hubble type and far infrared luminosity. Possible indications for a
correlation with inclination angle and the 60mum/100mum color temperature of
the dust are not significant. Higher R_{31} ratios than in ``normal'' galaxies,
hinting at enhanced molecular excitation, may be found in galaxies hosting
active galactic nuclei. Even higher average values are determined for galaxies
with bars or starbursts, the latter being identified by the ratio of infrared
luminosity versus isophotal area, log[(L_{FIR}/L_{SUN})/(D_{25}/kpc)^2)] >
7.25. (U)LIRGs are found to have the highest averaged R_{31} value. This may be
a consequence of particularly vigorous star formation activity, triggered by
galaxy interaction and merger events. The nuclear CO luminosities are slightly
sublinearly correlated with the global FIR luminosity in both the ^{12}CO J =
3-2 and the 1-0 lines. The slope of the log-log plots rises with compactness of
the respective galaxy subsample, indicating a higher average density and a
larger fraction of thermalized gas in distant luminous galaxies. While linear
or sublinear correlations for the ^{12}CO J = 3-2 line can be explained, if the
bulk of the observed J = 3-2 emission originates from molecular gas with
densities below the critical one, the case of the ^{12}CO J = 1-0 line with its
small critical density remains a puzzle.Comment: 26 pages, 9 figures, 4 tables, Accepted for publication in The
Astrophysical Journal (Part 1
Infrared two-colour diagrams for AGB stars using AKARI, MSX, IRAS and NIR data
Using a revised version of the catalog of AGB stars by Suh & Kwon (2009), we
present various infrared two-colour diagrams (2CDs) for 3003 O-rich, 1168
C-rich, 362 S-type and 35 silicate carbon stars in our Galaxy. For each object
in the new catalog, we cross-identify the AKARI, MSX and 2MASS counterparts by
finding the nearest one from the position information in the IRAS PSC. For the
large sample of AGB stars, we present infrared two-colour diagrams using IRAS
(PSC), AKARI (PSC and BSC), MSX (PSC) and near infrared (K and L bands;
including 2MASS data at KS band) data for different classes of AGB stars based
on the chemistry of the dust shell and/or the central star. The infrared 2CDs
of AGB stars can provide useful information about the structure and evolution
of the dust envelopes as well as the central stars. On the 2CDs, we plot tracks
of the theoretical radiative transfer model results with increasing dust shell
optical depths. Comparing the observations with the theoretical models on the
new 2CDs, we find that the basic model tracks roughly coincide with the densely
populated observed points. Generally, we can explain the observations of O-rich
and C-rich AGB stars on the various 2CDs with the theoretical models using dust
opacity functions of amorphous silicate, amorphous carbon, SiC and corundum.
For O-rich AGB stars, we find that the models using corundum as well as
silicate can improve the fit with the observations