The Stellar Content Near the Galactic Center

High angular resolution J, H, K, and L' images are used to investigate the stellar content within 6 arcsec of SgrA*. The data, which are complete to K ~ 16, are the deepest multicolor observations of the region published to date.Comment: 34 pages, including 12 figure

Astrometric performance of the Gemini multi-conjugate adaptive optics system in crowded fields

The Gemini Multi-conjugate adaptive optics System (GeMS) is a facility instrument for the Gemini-South telescope. It delivers uniform, near-diffraction-limited image quality at near-infrared wavelengths over a 2 arcminute field of view. Together with the Gemini South Adaptive Optics Imager (GSAOI), a near-infrared wide field camera, GeMS/GSAOI's combination of high spatial resolution and a large field of view will make it a premier facility for precision astrometry. Potential astrometric science cases cover a broad range of topics including exo-planets, star formation, stellar evolution, star clusters, nearby galaxies, black holes and neutron stars, and the Galactic center. In this paper, we assess the astrometric performance and limitations of GeMS/GSAOI. In particular, we analyze deep, mono-epoch images, multi-epoch data and distortion calibration. We find that for single-epoch, un-dithered data, an astrometric error below 0.2 mas can be achieved for exposure times exceeding one minute, provided enough stars are available to remove high-order distortions. We show however that such performance is not reproducible for multi-epoch observations, and an additional systematic error of ~0.4 mas is evidenced. This systematic multi-epoch error is the dominant error term in the GeMS/GSAOI astrometric error budget, and it is thought to be due to time-variable distortion induced by gravity flexure.Comment: 16 pages, 22 figures, accepted for publication in MNRA

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

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

Extragalactic Fields Optimized for Adaptive Optics

In this paper we present the coordinates of 67 55' x 55' patches of sky which have the rare combination of both high stellar surface density (>0.5 arcmin^{-2} with 13<R<16.5 mag) and low extinction (E(B-V)<0.1). These fields are ideal for adaptive-optics based follow-up of extragalactic targets. One region of sky, situated near Baade's Window, contains most of the patches we have identified. Our optimal field, centered at RA: 7h24m3s, Dec: -1deg27'15", has an additional advantage of being accessible from both hemispheres. We propose a figure of merit for quantifying real-world adaptive optics performance, and use this to analyze the performance of multi-conjugate adaptive optics in these fields. We also compare our results to those that would be obtained in existing deep fields. In some cases adaptive optics observations undertaken in the fields given in this paper would be orders of magnitude more efficient than equivalent observations undertaken in existing deep fields.Comment: 28 pages, 15 figures, 1 table; accepted for publication in PAS

The stellar mass - size relation for cluster galaxies at z=1 with high angular resolution from the Gemini/GeMS multi-conjugate adaptive optics system

We present the stellar mass - size relation for 49 galaxies within the $z$ = 1.067 cluster SPT-CL J0546$-$5345, with FWHM $\sim$80-120 mas $K_{\mathrm s}$-band data from the Gemini multi-conjugate adaptive optics system (GeMS/GSAOI). This is the first such measurement in a cluster environment, performed at sub-kpc resolution at rest-frame wavelengths dominated by the light of the underlying old stellar populations. The observed stellar mass - size relation is offset from the local relation by 0.21 dex, corresponding to a size evolution proportional to $(1+z)^{-1.25}$, consistent with the literature. The slope of the stellar mass - size relation $\beta$ = 0.74 $\pm$ 0.06, consistent with the local relation. The absence of slope evolution indicates that the amount of size growth is constant with stellar mass. This suggests that galaxies in massive clusters such as SPT-CL J0546$-$5345 grow via processes that increase the size without significant morphological interference, such as minor mergers and/or adiabatic expansion. The slope of the cluster stellar mass - size relation is significantly shallower if measured in $HST$/ACS imaging at wavelengths blueward of the Balmer break, similar to rest-frame UV relations at $z$ = 1 in the literature. The stellar mass - size relation must be measured at redder wavelengths, which are more sensitive to the old stellar population that dominates the stellar mass of the galaxies. The slope is unchanged when GeMS $K_s$-band imaging is degraded to the resolution of $K$-band HST/NICMOS resolution but dramatically affected when degraded to $K_s$-band Magellan/FourStar resolution. Such measurements must be made with AO in order to accurately characterise the sizes of compact, $z$ = 1 galaxies.Comment: 24 pages, 13 figures, 3 tables. Accepted for publication in MNRAS. Typos corrected, DOI adde

A disrupted circumstellar torus inside eta Carinae's Homunculus Nebula

We present thermal infrared images of the bipolar nebula surrounding eta Carinae at six wavelengths from 4.8 to 24.5 microns. These were obtained with the MIRAC3 camera system at the Magellan Observatory. Our images reveal new intricate structure in the bright core of the nebula, allowing us to re-evaluate interpretations of morphology seen in images with lower resolution. Complex structures in the core might not arise from a pair of overlapping rings or a cool (110 K) and very massive dust torus, as has been suggested recently. Instead, it seems more likely that the arcs and compact knots comprise a warm (350 K) disrupted torus at the intersection of the larger polar lobes. Some of the arcs appear to break out of the inner core region, and may be associated with equatorial features seen in optical images. The torus could have been disrupted by a post-eruption stellar wind, or by ejecta from the Great Eruption itself if the torus existed before that event. Kinematic data are required to rule out either possibility.Comment: 8 pages, 3 figures (Fig. 1 in color); to appear in ApJ Letter

NICI: combining coronagraphy, ADI, and SDI

The Near-Infrared Coronagraphic Imager (NICI) is a high-contrast AO imager at the Gemini South telescope. The camera includes a coronagraphic mask and dual channel imaging for Spectral Differential Imaging (SDI). The instrument can also be used in a fixed Cassegrain Rotator mode for Angular Differential Imaging (ADI). While coronagraphy, SDI, and ADI have been applied before in direct imaging searches for exoplanets. NICI represents the first time that these 3 techniques can be combined. We present preliminary NICI commissioning data using these techniques and show that combining SDI and ADI results in significant gains.Comment: Proc. SPIE, Vol. 7014, 70141Z (2008

Adaptive Optics for Astronomy

Adaptive Optics is a prime example of how progress in observational astronomy can be driven by technological developments. At many observatories it is now considered to be part of a standard instrumentation suite, enabling ground-based telescopes to reach the diffraction limit and thus providing spatial resolution superior to that achievable from space with current or planned satellites. In this review we consider adaptive optics from the astrophysical perspective. We show that adaptive optics has led to important advances in our understanding of a multitude of astrophysical processes, and describe how the requirements from science applications are now driving the development of the next generation of novel adaptive optics techniques.Comment: to appear in ARA&A vol 50, 201