70 research outputs found
Gemini Near-IR Photometry of the Arches Cluster near the Galactic Center
We present Near-IR photometry of the Arches cluster, a young and massive
stellar cluster near the Galactic center. We have analyzed the high resolution
(FWHM 0.2") H and K' band images in the Galactic Center Demonstration Science
Data Set, which were obtained with the Gemini/Hokupa's adaptive optics (AO)
system. We present the color-magnitude diagram, the luminosity function and the
initial mass function (IMF) of the stars in the Arches cluster in comparison
with the HST/NICMOS data. The IMF slope for the range of 1.0< log(M/M_sun) <2.1
is estimated to be Gamma = -0.79+/-0.16, in good agreements with the earlier
result based on the HST/NICMOS data [Figer et al. 1999, ApJ, 525, 750]. These
results strengthen the evidence that the IMF of the bright stars close to the
Galactic center is much flatter than that for the solar neighborhood. This is
also consistent with a recent finding that the IMFs of the bright stars in
young clusters in M33 get flatter as the galactocentric distance decreases [Lee
et al. 2001, astro-ph 0109258]. It is found that the power of the Gemini/AO
system is comparable, with some limits, to that of the HST/NICMOS.Comment: 11 pages, 6 figures, Accepted by the Journal of Korea Astronomy
Society (JKAS
Different Characteristics of the Bright Branches of the Globular Clusters M3 and M13
We carried out wide-field BVI CCD photometric observations of the GCs M3 and
M13 using the BOAO 1.8 m telescope equipped with a 2K CCD. We present CMDs of
M3 and M13. We have found AGB bumps at V = 14.85 for M3 at V = 14.25 for M13.
It is found that AGB stars in M3 are more concentrated near the bump, while
those in M13 are scattered along the AGB sequence. We identified the RGB bump
of M3 at V = 15.50 and that of M13 at V = 14.80. We have estimated the ratios R
and R2 for M3 and M13 and found that of R for M3 is larger than that for M13
while R2's for M3 and M13 are similar when only normal HB stars are used in R
and R2 for M13. However, we found that R's for M3 and M13 are similar while R2
for M3 is larger than that for M13 when all the HB stars are included in R and
R2 for M13. We have compared the observed RGB LFs of M3 and M13 with the
theoretical RGB LF of Bergbusch & VandenBerg at the same radial distances from
the cluster centers as used in R and R2 for M3 and M13. We found "extra stars"
belonging to M13 in the comparison of the observed RGB LF of M13 and the
theoretical RGB LF of Bergbusch & VandenBerg. In the original definition of R
of Buzzoni et al., N(HB) corresponds to the lifetime of HB stars in the RR
Lyrae instability strip at log T_eff = 3.85. So, the smaller R value resulting
for M13 compared with that for M3 in the case where only normal HB stars are
included in R and R2 for M13 may be partially caused by "extra stars", and the
similar R's for M3 and M13 in the case where the all HB stars are included in R
and R2 for M13 may be caused by "extra stars" in the upper RGB of M13. If
"extra stars" in the upper RGB of M13 are caused by an effective "deep mixing"
these facts support the contention that an effective "deep mixing" could lead
to different HB morphologies between M3 and M13 and subsequent sequences.Comment: 24 pages, 7 figures, to be published in the A
The Globular Cluster System of M60 (NGC 4649). I. CFHT MOS Spectroscopy and Database
We present the measurement of radial velocities for globular clusters in M60,
giant elliptical galaxy in the Virgo cluster. Target globular cluster
candidates were selected using the Washington photometry based on the deep
16\arcmin \times 16\arcmin images taken at the KPNO 4m and using the
photometry derived from the HST/WFPC2 archive images. The spectra of the target
objects were obtained using the Multi-Object Spectrograph (MOS) at the
Canada-France-Hawaii Telescope (CFHT). We have measured the radial velocity for
111 objects in the field of M60: 93 globular clusters (72 blue globular
clusters with and 21 red globular clusters with
), 11 foreground stars, 6 small galaxies, and the nucleus of
M60. The measured velocities of the 93 globular clusters range from
km s to km s, with a mean value of
km s, which is in good agreement with the velocity of the nucleus of M60
( km s). Combining our results with data in the
literature, we present a master catalog of radial velocities for 121 globular
clusters in M60. The velocity dispersion of the globular clusters in the master
catalog is found to be km s for the entire sample,
km s for 83 blue globular clusters, and
km s for 38 red globular clusters.Comment: 29 pages, 8 figures. To appear in Ap
The Globular Cluster System of M60 (NGC 4649). II. Kinematics of the Globular Cluster System
We present a kinematic analysis of the globular cluster (GC) system in the
giant elliptical galaxy (gE) M60 in the Virgo cluster. Using the photometric
and spectroscopic database of 121 GCs (83 blue GCs and 38 red GCs), we have
investigated the kinematics of the GC system. We have found that the M60 GC
system shows a significant overall rotation. The rotation amplitude of the blue
GCs is slightly smaller than or similar to that of the red GCs, and their
angles of rotation axes are similar. The velocity dispersions about the mean
velocity and about the best fit rotation curve for the red GCs are marginally
larger than those for the blue GCs. Comparison of observed stellar and GC
velocity dispersion profiles with those calculated from the stellar mass
profile shows that the mass-to-light ratio should be increased as the
galactocentric distance increases, indicating the existence of an extended dark
matter halo. The entire sample of GCs in M60 is found to have a tangentially
biased velocity ellipsoid unlike the GC systems in other gEs. Two subsamples
appear to have different velocity ellipsoids. The blue GC system has a modest
tangentially biased velocity ellipsoid, while the red GC system has a modest
radially biased or an isotropic velocity ellipsoid. From the comparison of the
kinematic properties of the M60 GC system to those of other gEs (M87, M49, NGC
1399, NGC 5128, and NGC 4636), it is found that the velocity dispersion of the
blue GC system is similar to or larger than that of the red GC system except
for M60, and the rotation of the GC system is not negligible. The entire sample
of each GC system shows an isotropic velocity ellipsoid except for M60, while
the subsamples show diverse velocity ellipsoids. We discuss the implication of
these results for the formation models of the GC system in gEs.Comment: 48 pages, 16 figures. To appear in Ap
High Resolution Optical and NIR Spectra of HBC 722
We present the results of high resolution (R30,000) optical and near-IR
spectroscopic monitoring observations of HBC 722, a recent FU Orionis object
that underwent an accretion burst in 2010. We observed HBC 722 in
optical/near-IR with the BOES, HET-HRS, and IGRINS spectrographs, at various
points in the outburst. We found atomic lines with strongly blueshifted
absorption features or P Cygni profiles, both evidence of a wind driven by the
accretion. Some lines show a broad double-peaked absorption feature, evidence
of disk rotation. However, the wind-driven and disk-driven spectroscopic
features are anti-correlated in time; the disk features became strong as the
wind features disappeared. This anti-correlation might indicate that the
rebuilding of the inner disk was interrupted by the wind pressure during the
first two years. The Half-Width at Half-Depth (HWHD) of the double-peaked
profiles decreases with wavelength, indicative of the Keplerian rotation; the
optical spectra with the disk feature are fitted by a G5 template stellar
spectrum convolved with a rotation velocity of 70 km s while the near-IR
disk features are fitted by a K5 template stellar spectrum convolved with a
rotation velocity of 50 km s. Therefore, the optical and near-IR spectra
seem to trace the disk at 39 and 76 , respectively. We fit
a power-law temperature distribution in the disk, finding an index of 0.8,
comparable to optically thick accretion disk models.Comment: 22 pages, 5 figures, accepted for publication in Ap
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