12 research outputs found
Halo globular clusters observed with AAOmega: dark matter content, metallicity and tidal heating
Globular clusters have proven to be essential to our understanding of many
important astrophysical phenomena. Here we analyse spectroscopic observations
of ten Halo globular clusters to determine their dark matter content, their
tidal heating by the Galactic disc and halo, describe their metallicities and
the likelihood that Newtonian dynamics explain their kinematics. We analyse a
large number of members in all clusters, allowing us to address all these
issues together, and we have included NGC 288 and M30 to overlap with previous
studies. We find that any flattening of the velocity dispersion profiles in the
outer regions of our clusters can be explained by tidal heating. We also find
that all our GCs have M/L_V < 5, therefore, we infer the observed dynamics do
not require dark matter, or a modification of gravity. We suggest that the lack
of tidal heating signatures in distant clusters indicates the Halo is not
triaxial. The isothermal rotations of each cluster are measured, with M4 and
NGC 288 exhibiting rotation at a level of 0.9 +/- 0.1 km/s and 0.25 +/- 0.15
km/s, respectively. We also indirectly measure the tidal radius of NGC 6752,
determining a more realistic figure for this cluster than current literature
values. Lastly, an unresolved and intriguing puzzle is uncovered with regard to
the cooling of the outer regions of all ten clusters.Comment: 12 pages, 8 figures, 1 table. Accepted for publication in MNRAS
The InfraRed Imaging Spectrograph (IRIS) for TMT: latest science cases and simulations
The Thirty Meter Telescope (TMT) first light instrument IRIS (Infrared
Imaging Spectrograph) will complete its preliminary design phase in 2016. The
IRIS instrument design includes a near-infrared (0.85 - 2.4 micron) integral
field spectrograph (IFS) and imager that are able to conduct simultaneous
diffraction-limited observations behind the advanced adaptive optics system
NFIRAOS. The IRIS science cases have continued to be developed and new science
studies have been investigated to aid in technical performance and design
requirements. In this development phase, the IRIS science team has paid
particular attention to the selection of filters, gratings, sensitivities of
the entire system, and science cases that will benefit from the parallel mode
of the IFS and imaging camera. We present new science cases for IRIS using the
latest end-to-end data simulator on the following topics: Solar System bodies,
the Galactic center, active galactic nuclei (AGN), and distant
gravitationally-lensed galaxies. We then briefly discuss the necessity of an
advanced data management system and data reduction pipeline.Comment: 15 pages, 7 figures, SPIE (2016) 9909-0
The GALEX Ultraviolet Atlas of Nearby Galaxies
We present images, integrated photometry, surface-brightness and color
profiles for a total of 1034 nearby galaxies recently observed by the GALEX
satellite in its far-ultraviolet (FUV; 1516A) and near-ultraviolet (NUV; 2267A)
bands. (...) This data set has been complemented with archival optical,
near-infrared, and far-infrared fluxes and colors. We find that the integrated
(FUV-K) color provides robust discrimination between elliptical and
spiral/irregular galaxies and also among spiral galaxies of different
sub-types. Elliptical galaxies with brighter K-band luminosities (i.e. more
massive) are redder in (NUV-K) color but bluer in (FUV-NUV) than less massive
ellipticals. In the case of the spiral/irregular galaxies our analysis shows
the presence of a relatively tight correlation between the (FUV-NUV) color and
the total infrared-to-UV ratio. The correlation found between (FUV-NUV) color
and K-band luminosity (with lower luminosity objects being bluer than more
luminous ones) can be explained as due to an increase in the dust content with
galaxy luminosity.
The images in this Atlas along with the profiles and integrated properties
are publicly available through a dedicated web page at
http://nedwww.ipac.caltech.edu/level5/GALEX_Atlas/Comment: 181 pages, 10 figures, accepted for publication in ApJS (abstract
abridged
Modern optical astronomy: technology and impact of interferometry
The present `state of the art' and the path to future progress in high
spatial resolution imaging interferometry is reviewed. The review begins with a
treatment of the fundamentals of stellar optical interferometry, the origin,
properties, optical effects of turbulence in the Earth's atmosphere, the
passive methods that are applied on a single telescope to overcome atmospheric
image degradation such as speckle interferometry, and various other techniques.
These topics include differential speckle interferometry, speckle spectroscopy
and polarimetry, phase diversity, wavefront shearing interferometry,
phase-closure methods, dark speckle imaging, as well as the limitations imposed
by the detectors on the performance of speckle imaging. A brief account is
given of the technological innovation of adaptive-optics (AO) to compensate
such atmospheric effects on the image in real time. A major advancement
involves the transition from single-aperture to the dilute-aperture
interferometry using multiple telescopes. Therefore, the review deals with
recent developments involving ground-based, and space-based optical arrays.
Emphasis is placed on the problems specific to delay-lines, beam recombination,
polarization, dispersion, fringe-tracking, bootstrapping, coherencing and
cophasing, and recovery of the visibility functions. The role of AO in
enhancing visibilities is also discussed. The applications of interferometry,
such as imaging, astrometry, and nulling are described. The mathematical
intricacies of the various `post-detection' image-processing techniques are
examined critically. The review concludes with a discussion of the
astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics,
2002, to appear in April issu
Adaptive Optics Observations of Stars in Globular Clusters and Nearby Galaxies
NRC publication: Ye
The Star Formation Histories of the Bulge and Disk of M31 from Resolved Stars in the Near-Infrared
NRC publication: Ye