84 research outputs found
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
Mapping dust column density in dark clouds by using NIR scattered light : Case of the Lupus 3 dark cloud
We present a method of mapping dust column density in dark clouds by using
near-infrared scattered light. Our observations of the Lupus 3 dark cloud
indicate that there is a well defined relation between (1) the H-Ks color of an
individual star behind the cloud, i.e., dust column density, and (2) the
surface brightness of scattered light toward the star in each of the J, H, and
Ks bands. In the relation, the surface brightnesses increase at low H-Ks
colors, then saturate and decrease with increasing H-Ks. Using a simple
one-dimensional radiation transfer model, we derive empirical equations which
plausibly represent the observed relationship between the surface brightness
and the dust column density. By using the empirical equations, we estimate dust
column density of the cloud for any directions toward which even no background
stars are seen. We obtain a dust column density map with a pixel scale of 2.3 x
2.3 arcsec^2 and a large dynamic range up to Av = 50 mag. Compared to the
previous studies by Juvela et al., this study is the first to use color excess
of the background stars for calibration of the empirical relationship and to
apply the empirical relationship beyond the point where surface brightness
starts to decrease with increasing column density
Interstellar Extinction Law toward the Galactic Center II: V, J, H, and Ks Bands
We have determined the ratios of total to selective extinction directly from
observations in the optical V band and near-infrared J band toward the Galactic
center. The OGLE (Optical Gravitational Lensing Experiment) Galactic bulge
fields have been observed with the SIRIUS camera on the IRSF telescope, and we
obtain A(V)/E(V-J)=1.251+-0.014 and A(J)/E(V-J)=0.225+-0.007. From these
ratios, we have derived A(J)/A(V) = 0.188+-0.005; if we combine A(J)/A(V) with
the near-infrared extinction ratios obtained by Nishiyama et al. for more
reddened fields near the Galactic center, we get A(V) : A(J) : A(H) : A(Ks) = 1
: 0.188 : 0.108 : 0.062, which implies steeply declining extinction toward the
longer wavelengths. In particular, it is striking that the Ks band extinction
is \approx 1/16 of the visual extinction A(V) much smaller than one tenth of
A(V) so far employed.Comment: 8 pages, 7 figures, Accepted for publication in Ap
Near-Infrared Extinction in The Coalsack Globule 2
We have conducted J, H, and Ks imaging observations for the Coalsack Globule
2 with the SIRIUS infrared camera on the IRSF 1.4 m telescope at SAAO, and
determined the color excess ratio, E(J-H)/E(H-Ks). The ratio is determined in
the same photometric system as our previous study for the rho Oph and Cha
clouds without any color transformation; this enables us to directly compare
the near-infrared extinction laws among these regions. The current ratio
E(J-H)/E(H-Ks) = 1.91 +- 0.01 for the extinction range 0.5 < E(J-H) <1.8 is
significantly larger than the ratios for the rho Oph and Cha clouds
(E(J-H)/E(H-Ks) = 1.60-1.69). This ratio corresponds to a large negative index
alpha = 2.34 +- 0.01 when the wavelength dependence of extinction is
approximated by a power law which might indicate little growth of dust grains,
or larger abundance of dielectric non-absorbing components such as silicates,
or both in this cloud. We also confirm that the color excess ratio for the
Coalsack Globule 2 has a trend of increasing with decreasing optical depth,
which is the same trend as the rho Oph and Cha clouds have.Comment: 13 pages, 5 figures, and 2 tables, Ap
Clustering of Emission-line Stars in the W5E HII region
We have made a new survey of emission-line stars in the W5E HII region to
investigate the population of PMS stars near the OB stars by using the Wide
Field Grism Spectrograph 2 (WFGS2). A total of 139 H-alpha emission stars were
detected and their g'i'-photometry was performed. The spatial distribution of
them shows three aggregates, i.e., two aggregates near the bright-rimmed clouds
at the edge of W5E HII region (BRC 13 and BRC 14) and one near the exciting O7V
star. The age and mass of each H-alpha star were estimated from the extinction
corrected color-magnitude diagram and theoretical evolutionary tracks. We
found, for the first time in this region, that the young stars near the
exciting star are systematically older (4 Myr) than those near the edge of the
HII region (1 Myr). This result supports that the formation of stars proceed
sequentially from the center of HII region to the eastern bright rim. We
further suggest a possibility that the birth of low mass stars near the
exciting star of HII region precede the production of massive OB stars in the
pre-existing molecular cloud.Comment: 16 pages, 7 figures, 3 tables, accepted for publication in PAS
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