192 research outputs found
Infrared Search for Young Brown Dwarf Companions around Young Stellar Objects in the rho Ophiucus Molecular Cloud and the Serpens Molecular Cloud
We conducted an infrared search for faint companions around 351 young stellar
objects in the rho Ophiucus molecular cloud and the Serpens molecular cloud.
Nine objects in the Spitzer/IRAC archival images were identified as young
stellar companion candidates. They showed an intrinsic infrared excess; one
object was extremely red both in the [3.6] - [4.5] color and in the [4.5] -
[5.8] color, and two objects were red in the [4.5] - [5.8] color. They were as
faint as 15 mag in the [3.6] band. Follow-up K-band spectroscopy revealed that
three objects had deep water absorption bands, indicative of low effective
temperatures. By comparing the spectra and infrared spectral energy
distributions with synthesized spectra of low-temperature objects, we derived
the effective temperatures and continuum excess for these objects. It seems
highly likely that one of the three objects is a low-mass stellar companion and
two objects are young brown dwarf companions associated with the young stellar
objects.Comment: 11 pages, 7 figures. P.A.S.J. accepte
Age Determination Method of Pre-Main Sequence Stars with High-Resolution I-Band Spectroscopy
We present a new method for determining the age of late-K type pre-main
sequence (PMS) stars by deriving their surface gravity from high-resolution
I-band spectroscopy. Since PMS stars contract as they evolve, age can be
estimated from surface gravity. We used the equivalent width ratio (EWR) of
nearby absorption lines to create a surface gravity diagnostic of PMS stars
that is free of uncertainties due to veiling. The ratios of Fe (818.67nm and
820.49nm) and Na (818.33nm and 819.48nm) absorption lines were calculated for
giants, main-sequence stars, and weak-line T Tauri stars. Effective
temperatures were nearly equal across the sample. The Fe to Na EWR (Fe/Na)
decreases significantly with increasing surface gravity, denoting that Fe/Na is
a desirable diagnostic for deriving the surface gravity of pre-main sequence
stars. The surface gravity of PMS stars with 0.8 solar mass is able to be
determined with an accuracy of 0.1-0.2, which conducts the age of PMS stars
within a factor of 1.5, in average.Comment: 16 pages, 5 figures, 3 tables, accepted for publication in PAS
Sequential Formation of Low-Mass Stars in the BRC 14 Region
We have carried out a deep near-infrared survey of a bright-rimmed molecular
cloud, BRC 14 (IC 1848A). The 10 sigma limiting magnitude of the survey is 17.7
mag at the K-band. Seventy-four sources are classified as young stellar object
(YSO) candidates based on the near-infrared color-color diagram. The faintest
YSO candidates may have masses of an order of tenths of the solar mass,
assuming the age of 1 Myr. We examined three values as indicators of star
formation; fraction of the YSO candidates, extinctions of all sources, and
near-infrared excesses of the YSO candidates. All indicators increase from
outside of the rim to the center of the molecular cloud, which suggests that
the formation of the low-mass stars in the BRC 14 region proceeds from outside
to the center of the cloud.Comment: 12 pages, 5 figures, 1 table, PASJ accepte
SUBARU Near-Infrared Multi-Color Images of Class II Young Stellar Object, RNO91
We conducted sub-arcsecond near-infrared imaging observations of RNO91 with
CIAO mounted on the SUBARU 8.2 m telescope. We present our JHK band data along
with optical images, which when considered together reveal a complex
circumstellar structure. We examined the colors of associated nebula and
compared the geometry of the outflow/disk system suggested by our data with
that already proposed on the basis of previous studies. Our K-band image shows
bright circumstellar nebulosity detected within 2"(300AU) around the central
source while it is less conspicuous at shorter wavelengths such as J and
optical. P.A. and size of this red color nebulosity in our H-K color image
agree with those of the previously detected polarization disk. These data
agreement indicate that this bright circumstellar nebulosity region which
follows the reddening law might be attributed to a disk-like structure. At J
and optical wavelengths, several blue knot-like structures are detected around
and beyond the bright circumstellar nebulosity. We suggest that these knotty
reflection nebulae may represent disintegrating fragments of an infalling
envelope. The three-color composite image has an appearance of arc-shaped
nebulosity extending to the north and to the east through the central source.
On the other end of this arc-shaped structure, the nebula appears to become
more extended (2."3 long) to the southwest. We interpret these structures as
roots of bipolar cavities opening to the northeast and southwest. The complex
distribution of reflection nebulosity seen around RNO91 appears to confirm the
interpretation of this source as an object dispersing its molecular envelope
while transitioning from protostar to T Tauri star.Comment: 18 pages, 6 figures, Accepted by Publications of the Astronomical
Society of Japa
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