56 research outputs found
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
A Chain of Dark Clouds in Projection Against the Galactic Center
In the J, H, and Ks bands survey of the the Galactic Center region over an
area of 2deg x 5deg, we have found many dark clouds, among which a
distinguished chain of dark clouds can be identified with a quiescent CO cloud.
The distances of the clouds is estimated to be 3.2-4.2 kpc, corresponding to
the Norma arm by our new method to determine distance to dark clouds using the
cumulative number of stars against J-Ks colors. Adopting these estimated
distances, the size is about 70 pc in length and the total mass of the cloud is
6x10^4 M_solar. Three compact HII regions harbor in the cloud, indicating that
star forming activities are going on at the cores of the quiescent CO cloud on
the spiral arm.Comment: 13 pages, 7 figures, accepted for publication in PAS
Herbig Ae/Be Stars in the Magellanic Bridge
We have found Herbig Ae/Be star candidates in the western region of the
Magellanic Bridge. Using the near infrared camera SIRIUS and the 1.4 m
telescope IRSF, we surveyed about 3.0 deg x 1.3 deg (24 deg < RA < 36 deg, -75
deg < Dec. < -73.7 deg) in the J, H, and Ks bands. On the basis of colors and
magnitudes, about 200 Herbig Ae/Be star candidates are selected. Considering
the contaminations by miscellaneous sources such as foreground stars and
early-type dwarfs in the Magellanic Bridge, we estimate that about 80 (about
40%) of the candidates are likely to be Herbig Ae/Be stars. We also found one
concentration of the candidates at the young star cluster NGC 796, strongly
suggesting the existence of pre-main-sequence (PMS) stars in the Magellanic
Bridge. This is the first detection of PMS star candidates in the Magellanic
Bridge, and if they are genuine PMS stars, this could be direct evidence of
recent star formation. However, the estimate of the number of Herbig Ae/Be
stars depends on the fraction of classical Be stars, and thus a more precise
determination of the Be star fraction or observations to differentiate between
the Herbig Ae/Be stars and classical Be stars are required.Comment: 22 pages, 6 figures. Accepted for publication in Ap
Interstellar Extinction Law toward the Galactic Center III: J, H, Ks bands in the 2MASS and the MKO systems, and 3.6, 4.5, 5.8, 8.0 micron in the Spitzer/IRAC system
We have determined interstellar extinction law toward the Galactic center
(GC) at the wavelength from 1.2 to 8.0 micron, using point sources detected in
the IRSF/SIRIUS near-infrared survey and those in the 2MASS and
Spitzer/IRAC/GLIMPSE II catalogs. The central region |l| < 3deg and |b| < 1deg
has been surveyed in the J, H and Ks bands with the IRSF telescope and the
SIRIUS camera whose filters are similar to the Mauna Kea Observatories (MKO)
near-infrared photometric system. Combined with the GLIMPSE II point source
catalog, we made Ks versus (Ks - lambda) color-magnitude diagrams where lambda
= 3.6, 4.5, 5.8, and 8.0 micron. The Ks magnitudes of bulge red clump stars and
the (Ks - lambda) colors of red giant branches are used as a tracer of the
reddening vector in the color-magnitude diagrams. From these magnitudes and
colors, we have obtained the ratios of total to selective extinction
A(Ks)/E(Ks-lambda) for the four IRAC bands. Combined with A(lambda)/A(Ks) for
the J and H bands derived by Nishiyama et al., we obtain
A(J):A(H):A(Ks):A([3.6]):A([4.5]):A([5.8]):A([8.0])=3.02:1.73:1:0.50:0.39:0.36:0.43
for the line of sight toward the GC. This confirms the flattening of the
extinction curve at lambda > 3 micron from a simple extrapolation of the
power-law extinction at shorter wavelengths, in accordance with recent studies.
The extinction law in the 2MASS JHKs bands has also been calculated, and a good
agreement with that in the MKO system is found. In nearby molecular clouds and
diffuse interstellar medium, the lack of reliable measurements of the total to
selective extinction ratios hampers unambiguous determination of the extinction
law; however, observational results toward these lines of sight cannot be
reconciled with a single extinction law.Comment: 27 pages, 10 figures, Accepted for publication in Ap
A near-infrared survey of Miras and the distance to the Galactic Centre
We report the results of a near-infrared survey for long-period variables in
a field of view of 20 arcmin by 30 arcmin towards the Galactic Centre (GC). We
have detected 1364 variables, of which 348 are identified with those reported
in Glass et al. (2001). We present a catalogue and photometric measurements for
the detected variables and discuss their nature. We also establish a method for
the simultaneous estimation of distances and extinctions using the
period-luminosity relations for the JHKs bands. Our method is applicable to
Miras with periods in the range 100--350 d and mean magnitudes available in two
or more filter bands. While J-band means are often unavailable for our objects
because of the large extinction, we estimated distances and extinctions for 143
Miras whose H- and Ks-band mean magnitudes are obtained. We find that most are
located at the same distance to within our accuracy. Assuming that the
barycentre of these Miras corresponds to the GC, we estimate its distance
modulus to be 14.58+-0.02(stat.)+-0.11(syst.) mag, corresponding to
8.24+-0.08(stat.)+-0.42(syst.) kpc. We have assumed the distance modulus to the
LMC to be 18.45 mag, and the uncertainty in this quantity is included in the
systematic error above. We also discuss the large and highly variable
extinction. Its value ranges from 1.5 mag to larger than 4 mag in A(Ks) except
towards the thicker dark nebulae and it varies in a complicated way with the
line of sight. We have identified mid-infrared counterparts in the Spitzer/IRAC
catalogue of Ramirez et al. (2008) for most of our variables and find that they
follow rather narrow period-luminosity relations in the 3.6 to 8.0 micrometre
wavelength range.Comment: Accepted for publication in MNRAS, 22 pages (28 tables, 11 figures).
Figure 7 and tables 6, 7 and 9 will be published in full online onl
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