88 research outputs found
Gemini Frontier Fields: Wide-field Adaptive Optics -band Imaging of the Galaxy Clusters MACS J0416.1-2403 and Abell 2744
We have observed two of the six Frontier Fields galaxy clusters, MACS
J0416.1-2403 and Abell 2744, using the Gemini Multi-Conjugate Adaptive Optics
System (GeMS) and the Gemini South Adaptive Optics Imager (GSAOI). With
0.08"-0.10" FWHM our data are nearly diffraction-limited over a 100"x100" wide
area. GeMS/GSAOI complements the Hubble Space Telescope (HST) redwards of
1.6microns with twice the angular resolution. We reach a 5 sigma depth of Ks =
25.6 mag (AB) for compact sources. In this paper we describe the observations,
the data processing and the initial public data release. We provide fully
calibrated, co-added images matching the native GSAOI pixel scale as well as
the larger plate scales of the HST release, adding to the legacy value of the
Frontier Fields. Our work demonstrates that even for fields at high galactic
latitude, where natural guide stars are rare, current multi-conjugated adaptive
optics technology at 8m-telescopes has opened a new window on the distant
Universe. Observations of a third Frontier Field, Abell 370, are planned.Comment: Accepted for publication in ApJS; significantly revised compared to
the first submissio
Haffner 16: A Young Moving Group in the Making
The photometric properties of main sequence (MS) and pre-main sequence (PMS)
stars in the young cluster Haffner 16 are examined using images recorded with
the Gemini South Adaptive Optics Imager (GSAOI) and corrected for atmospheric
blurring by the Gemini Multi-Conjugate Adapative Optics System (GeMS). A rich
population of PMS stars is identified, and comparisons with isochrones suggest
an age < 10 Myr assuming a distance modulus of 13.5 (D = 5 kpc). When compared
with the solar neighborhood, Haffner 16 is roughly a factor of two deficient in
objects with sub-solar masses. PMS objects in the cluster are also more
uniformly distributed on the sky than bright MS stars. It is suggested that
Haffner 16 is dynamically evolved, and that it is shedding protostars with
sub-solar masses. Young low mass clusters like Haffner 16 are one possible
source of PMS stars in the field. The cluster will probably evolve on time
scales of ~ 100 - 1000 Myr into a diffuse moving group with a mass function
that is very different from that which prevailed early in its life.Comment: To appear in the Publications of the Astronomical Society of the
Pacifi
Towards a calibration of SSP models from the optical to the mid-infrared
Our knowledge about unresolved stellar systems comes from comparing
integrated-light properties to SSP models. Therefore it is crucial to calibrate
the latter as well as possible by integrated-light colors of clusters that have
reliable ages and metallicities (deep CMDs and/or spectroscopy of individual
giants). This is especially true for the NIR and MIR, which contain important
population synthesis diagnostics and are often used to derive masses of stellar
systems at hight redshifts. Here we present integrated colors of MC clusters
using new VRI photometry and 2MASS data. In the imminent future we will include
MIR data from Spitzer/IRAC. We compare our new colors with popular SSP models
to illustrate their strengths and weaknesses.Comment: 2 pages, 1 figure, to appear in the proceedings of IAU Symposium
No241 "Stellar Populations as building blocks of galaxies", A. Vazdekis & R.
Peletier, ed
First performance of the gems + gmos system. Part1. Imaging
During the commissioning of the Gemini MCAO System (GeMS), we had the
opportunity to obtain data with the Gemini Multi-Object Spectrograph (GMOS),
the most utilised instrument at Gemini South Observatory, in March and May
2012. Several globular clusters were observed in imaging mode that allowed us
to study the performance of this new and untested combination. GMOS is a
visible instrument, hence pushing MCAO toward the visible.We report here on the
results with the GMOS instruments, derive photometric performance in term of
Full Width Half Maximum (FWHM) and throughput. In most of the cases, we
obtained an improvement factor of at least 2 against the natural seeing. This
result also depends on the Natural Guide Star constellation selected for the
observations and we then study the impact of the guide star selection on the
FWHM performance.We also derive a first astrometric analysis showing that the
GeMS+GMOS system provide an absolute astrometric precision better than 8mas and
a relative astrometric precision lower than 50 mas.Comment: 13 pages, 11 figures, accepted for publication in MNRAS on March 23rd
201
The Brightening of Re50N: Accretion Event or Dust Clearing?
The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is
associated with a pair of reflection nebulae, Re50 and Re50N, which appeared
sometime between 1955 and 1979. We have found that a dramatic brightening of
Re50N has taken place sometime between 2006 and 2014. This could result if the
embedded source is undergoing a FUor eruption. However, the near-infrared
spectrum shows a featureless very red continuum, in contrast to the strong CO
bandhead absorption displayed by FUors. Such heavy veiling, and the high
luminosity of the protostar, is indicative of strong accretion but seemingly
not in the manner of typical FUors. We favor the alternative explanation that
the major brightening of Re50N and the simultaneous fading of Re50 is caused by
curtains of obscuring material that cast patterns of illumination and shadows
across the surface of the molecular cloud. This is likely occurring as an
outflow cavity surrounding the embedded protostar breaks through to the surface
of the molecular cloud. Several Herbig-Haro objects are found in the region.Comment: 8 pages, accepted by Ap
Discovery of New Milky Way Star Clusters Candidates in the 2MASS Point Source Catalog
A systematic search of the 2MASS point source catalog, covering 47% of the
sky, was carried out aiming to reveal any hidden globular clusters in our
Galaxy. Eight new star clusters were discovered by a search algorithm based on
finding peaks in the apparent stellar surface density, and a visual inspection
of their vicinities yielded additional two. They all are concentrated toward
the Galactic plane and are hidden behind up to Av=20 mag which accounts for
their late discovery. The majority of new clusters are associated with H II
regions or unidentified IRAS sources suggesting that they are young, probably
similar to Arches or open clusters. Only one candidate has morphology similar
to a globular cluster and the verification of its nature will require deeper
observations with higher angular resolution than the 2MASS data.Comment: 4 pages, 3 figures (1 is a jpeg file), acccepted for publication in
Astronomy and Astrophysic
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