# 2002A Gemini South Queue Abstracts

Abstracts for all successful 2002A queue programs on Gemini South are given below.

GS-2002A-Q-1

Title: Oxygen abundance of the metal-rich bulge globular cluster NGC 6553

Abstract: The metal-rich globular clusters in the Galactic bulge are a keystone for the understanding of the formation of the bulge, which in turn has consequences on the scenarios of galaxy formation. We propose to carry out high resolution spectral observations in the H band of individual stars of the bulge globular cluster NGC 6553. W e have well-determined reddening and VIJK colours for this cluster, which permits a reliable determination of effective temperatures. We also have VLT-UVES optical spectra for the analysis of the same stars to be studied here. Besides we previously carried out a detailed analysis of two stars in this cluster using spectra from the 3.6m ESO telescope. We propose to derive the abundance of the alpha-element oxygen, based on OH lines located around 1.5555 mu. It has to be pointed out that, for this cluster, no other oxygen line is observable. The oxygen-to-iron ratio can give important hints on the timescale of bulge formation. In the last years we have developed a careful work of preparation of a list of atomic and molecular lines in the H band, and we have the necessary tool for such analysis

GS-2002A-Q-2

Title: Homogeneity of Cluster Elliptical Galaxies at z~1

Abstract: We propose to use GEMINI+FLAMINGOS to obtain deep J and K imaging in the central regions of 5 z~1 galaxy clusters, taken from the Red-sequence Cluster Survey. These data will be used to constrain the homogeneity in the integrated optical-IR colours of the cluster E/S0s, within each cluster and among the different clusters. These data will be combined with already existing optical imaging and with lower redshift photometry (to construct the optical-NIR colour evolution vector) and used to constrain the predictions of popular simple stellar population (SSP) models, particularly in the NIR. Quantitative morphology will allow us to segregate the early-type population and to study their size distributions. This program was awarded time at Gemini before, but problems with NIRI resulted in no observations at all.

GS-2002A-Q-3

Title: High Resolution Infrared Spectroscopy of L Dwarfs

Abstract: We propose high spectral resolution, 2.3 micrometre region observations of a sample of L dwarfs. Spectral features will be identified using extensive line lists developed for our solar and stellar atlas projects and using new laboratory and theoretical data for the H2O and CH4 molecules. A few late M dwarfs (M7-M10) and an early T dwarf will be observed to compare the M, L and T spectral types.

GS-2002A-Q-4

Title: Imaging extra-solar planets

Abstract: We propose to obtain deep, near-IR (J) images of young, nearby white dwarfs, to detect massive planetary companions (>3Mj). Since the white dwarfs are evolved from 1.5-4Msol stars, we will in effect be probing the frequency of massive companions to solar type (and more massive) stars. Radial velocity surveys are heavily biased towards massive, short period planets and provide little or no information on systems with massive planets at large radii, such as our own. Our observations will probe exactly this region. By targeting white dwarfs we will obtain better contrast and angular separation (due to outward movement of the planets during primary mass loss) than surveys around main-sequence stars. These observations will, therefore, provide significant constraints on the frequency of massive planetary companions to solar-type (and more massive) stars, and potentially provide the first sample of extra-solar planets that can be directly observed.

GS-2002A-Q-5

Title: Search for Small-Scale Structure in Gamma-ray Burst Afterglows

Abstract: We propose to obtain high S/N optical photometry with rapid time sampling of bright ($R < 21$) gamma-ray burst afterglows in order to detect predicted small-scale fluctuations about the mean decay. Such deviations must be present at some level (1) due to inhomogeneities in the circumburst medium, and (2) if the afterglow is refreshed'' by collisions among separate shells of ejecta (refreshed shocks). Detection of small-scale fluctuations and their interpretation within the context of the first mechanism would probe the immediate environment of the GRB progenitor, e.g., revealing a clumpy star-forming region or ISM turbulence. Detection of refreshed shocks would, for the first time, link the optical afterglow directly to the gamma-ray burst and affirm the internal-external shock model for GRBs. This is an ideal program to help develop the advertised Quick-Response observing mode using the Acquisition Camera on Gemini South by obtaining unique time-domain data on GRB afterglows.

GS-2002A-Q-6

Title: Imaging the heart of Centaurus A - the nature of the AGN

Abstract: We propose T-ReCS mid-infrared imaging observations of the nearest AGN, in Centaurus A. These images should differentiate for the first time the point-like BLLac core from the central nuclear torus, possibly about 15" in size. The field of view of a single frame includes both structures, together with some of the galaxy's inner thin disk. Dust temperatures for the torus are in the range 250 to 750K, and multi-filter observations are requested to determine the SED's of both components.

GS-2002A-Q-7

Title: Are the hosts of Gamma-Ray Bursts luminous starbursts or normal galaxies?

Abstract: Present knowledge indicates that most gamma-ray bursts (GRBs) are linked to the collapse of massive stars. Because gamma-rays are not attenuated by intervening dust and gas, the selection of the cosmic sites of massive star formation by this method is less affected by the biases associated with optical-uv surveys (e.g. UV-dropout technique). As a complement to the imaging and spectroscopic observations of southern GRB host galaxies that we have carried out in periods P67 and P68 with FORS and ISAAC on the VLT, we propose to perform low-resolution spectroscopy of northern GRB host galaxies on Gemini North. The immediate purpose of this program is to characterize the physical properties of GRB hosts, and to determine whether GRBs occur in normal galaxies. The crucial issue would lead, in the future, to use GRB occurance rate as a direct measurement of the cosmic star formation history even in dusty enshrouded regions.

GS-2002A-Q-8

Title: The Gas Dissipation Timescale in Protoplanetary Disks

Abstract: We propose to search for 4.7 micron CO fundamental emission from T Tauri stars in the age range $<1-10$ Myr in order to measure the gas dissipation timescale in protoplanetary disks. CO fundamental emission is a sensitive new probe of gas at planet formation distances ($r < 5$ AU) and an ideal tracer of a dissipating gas disk, since the fundamental lines are sensitive to even small amounts of gas at the expected temperatures of interest (300--1000 K). With a measurement of the gas dissipation timescale, we will be able to place fundamental constraints on theories of solar system and giant planet formation.

GS-2002A-Q-9

Title: Search for Small-Scale Structure in Gamma-Ray Burst Afterglows

Abstract: We propose to obtain high S/N optical photometry with rapid time sampling of bright (R < 21 mag) gamma-ray burst afterglows in order to detect predicted small-scale fluctuations about the mean decay. Such deviations must be present at some level (1) due to inhomogeneities in the circumburst medium, and (2) if the afterglow is refreshed'' by collisions among separate shells of ejecta (refreshed shocks). Detection of small-scale fluctuations and their interpretation within the context of the first mechanism would probe the immediate environment of the GRB progenitor, e.g., revealing a clumpy star-forming region or ISM turbulence. Detection of refreshed shocks would, for the first time, link the optical afterglow directly to the gamma-ray burst and affirm the internal-external shock model for GRBs. This is an ideal program to help develop the advertised Quick-Response observing mode using the Acquisition Camera on Gemini South by obtaining unique time-domain data on GRB afterglows.

GS-2002A-Q-10

Title: Structure of inner disks of young stars from fundamental CO emission

Abstract: The inner (r~1AU) circumstellar disks of young stars harbor optically thin gas that may reside in "gaps" created by protoplanet accretion or in a tenuous disk atmospheres. Although both are theorized to exist, the models are still immature and there is very little observational evidence to constrain them. The high spectral resolution (delta-v ~ 5 km/s) and high signal-to-noise (>50) achievable with Gemini+Phoenix can directly probe the region within a few AU of the star, where current spatial resolving power cannot. Analysis of the kinematics and excitation of fundamental emission lines of carbon monoxide, abundant in the near-infrared, can reveal the temperature and surface density of the emitting gas, and place strong constraints on the inner and outer radii (Carr et al. 2001). We propose to observe multiple transitions of fundamental CO emission in the 4.6 micron region from several young stars in the rho Ophiuchus and Chamaeleon clouds. Our goal is to determine the thermal and kinematic properties of optically thin gas at 1 AU distances for comparison with disk atmosphere and disk gap models, and assess the presence and radial distribution of inner disk gaps. These will be the first observations of this kind with sufficient resolution and sensitivity to begin to test the theories, and potentially open up new avenues for the detection and study of newly-forming protoplanets.

GS-2002A-Q-11

Title: The $^{16}$O/$^{17}$O Ratio in Halo Giants \\

Abstract: Although the abundance of oxygen is critical in numerous astrophysical contexts, its value at low metallicities is controversial. Four oxygen abundance indicators support two different trends of [O/Fe] with metallicity; OI and UV-OH lines indicate a monotonically increasing trend with decreasing metallicity while [OI] and IR-OH lines indicate a lower plateau at low metallicities. Although the latter trend has more robust abundance indicators, it is measured from giants whose surface abundances could be altered by the mixing-in of ON-cycle products, whereas the high oxygen trend is measured from dwarfs. In order to resolve this impasse, we propose to measure the $^{16}$O/$^{17}$O ratio in metal-poor field halo giants. Because it is independent of the initial oxygen abundance of the star, the oxgyen isotopic ratio will unambiguously determine whether or not the giants trace the Galactic evolution of oxygen.

GS-2002A-Q-12

Title: Probing the forming cores of galaxy clusters

Abstract: Studies of rich clusters to z=1 indicate that galaxies in their central regions finished forming the bulk of their stars at z>2, in contrast to field galaxies, which formed half of their stars since z=2. The difference in star formation history is due to the mechanics of forming the core of a cluster at high redshift, the details of which are not clear. Key to understanding this are studies of the galaxies at the centres of z>2 (proto) clusters, hampered by the fact that we have yet to discover a sample of such clusters! Blind optical, Xray and SZ surveys are several years away from generating samples of clusters at z>2. However, by targeting the environments of z>2 powerful radio loud AGN using FLAMINGOS, we aim to discover high redshift (proto) clusters that surround them and subsequently characterise the galaxy population in the forming cluster cores. We request time split 16:12:4 UK:CL:AU.

GS-2002A-Q-13

Title: The Stellar Density Around Massive Young Stars: A Test of

Abstract: We propose deep (23.2, 22.3, 22.1 mag. in JHK) observations of the NGC 6334 I region. This region contains three young massive stars, two of which are surrounded by a cluster of lower mass stars. With the exceptional sensitivity of Gemini, we can detect low mass stars in the vicinity of the three deeply embedded high mass (proto)stars, and obtain the first measurement of the stellar density within 0.02 pc of these massive stars. From this data, we will infer the rate of stellar collisions in a region of very recent massive star formation and test whether massive stars form through the collision and coalescence of lower mass stars.

GS-2002A-Q-14

Title: Probing the Halos of Late-type Spiral Galaxies in the Sculptor Group

Abstract: The metallicity distribution functions (MDFs) of stars in galactic halos provide a means of probing the early evolution of proto-galaxies. The MDF can be constructed from the CMD of resolved giants, and efforts to measure the MDF have so far been restricted to Local Group galaxies. I propose to use FLAMINGOS-I to obtain moderately deep J and Ks images of fields in the halos of the Sculptor Group spiral galaxies NGC 7793, NGC 55, and NGC 300, which are the closest spiral galaxies outside the Local Group, and use these data to measure the MDF of halo stars in these systems. Not only will these observations double the number of halos in which individual stars have been resolved, but it will also provide the first basis of comparison with the halos of Local Group galaxies, which show a rich diversity in chemical content. The galaxies have similar integrated brightnesses and morphological properties, and the detection of significant galaxy-to-galaxy differences in the MDF would support hierarchal merging models of halo formation. Near-infrared observations will allow a sample of stars to be defined that is unbiased according to metallicity, which is much more difficult to obtain with observations at visible wavelengths.

GS-2002A-Q-15

Title: Mid-Infrared Imaging of Disks of Transitional Herbig Ae/Be Stars

Abstract: We propose to use T-ReCS to image at 10 and 20 microns the dusty circumstellar disks of Herbig Ae/Be stars that appear to be at an evolutionary stage between the very young embedded Herbig stars and their main sequence progeny, the so-called Vega-type stars. By choosing this special sample of "transitional" stars that are approaching the ZAMS, we will be able to explore disks that are less than a million years old and at a very early phase of planet formation. Because these particular pre-main-sequence stars have evolved beyond the heavily embedded phase, most of the excess IR emission should be associated with disks rather than placental envelopes. Nevertheless, our high-angular-resolution, diffraction-limited imaging with T-ReCS should be able to distinguish disks from any significant extended residual envelope emission. A key goal is to spatially resolve the disks or place severe limits on the sizes of the mid-IR-emitting regions, the success of which is enhanced by the proximity (<200 pc) of most of these objects. As shown previously, disk structure such as holes, gaps, and asymmetries are critical clues to the evolution of disks and planetary systems. Limits on the source sizes can constrain dust particle temperatures and sizes and provide insight into the planetary growth process and evolutionary stage of the disk.

GS-2002A-Q-16

Title: High Resolution Infrared Spectroscopy of L Dwarfs

Abstract: We propose high spectral resolution, 2.3 $\mu$m region observations of a sample of L dwarfs. Spectral features will be identified using extensive line lists developed for our solar and stellar atlas projects and using new laboratory and theoretical data for the H$_2$O and CH$_4$ molecules. A few late M dwarfs (M7-M10) and an early T dwarf will be observed to compare the M, L and T spectral types. The relation between equivalent width and spectral type will be found for key spectral lines. This relation will be calibrated to effective temperature and gravity using synthetic spectra and recent model atmospheres. The CO and atomic (Na) spectral features will be used to measure the rotation and magnetic fields of these dwarfs. We will also search for individual methane lines marking the first formation of methane in the outer atmospheres of these ultracool dwarfs.

GS-2002A-Q-17

Title: Direct Measurement of Cold H$_2$ and CO \\in the $\rho$ Ophiuchus Star Forming Region

Abstract: High-resolution infrared spectroscopy provides a powerful probe of the physical conditions, abundances, chemistry and distribution of molecular material in interstellar clouds. In particular, the abundance and excitation of {\bf cold} H$_2$ and CO gas in molecular clouds and star forming regions can be measured in absorption {\it} directly along milli-arcsecond pencil beam'' lines of sight. Indeed, the need for sensitive, high-resolution absorption spectroscopy of interstellar matter has been one of the important scientific justifications for constructing the Phoenix spectrometer. In particular, through a weak quadrupole line spectrum, the pivotal H$_2$ molecule can be {\bf directly} detected and compared along the same pencil-beam line of sight with the abundance of its most commonly cited surrogate, CO. The excitation and abundances of these two species are being firmly established by this group via observations with Phoenix at Kitt Peak. With the improved sensitivity and high resolution of Phoenix at Gemini, coarse mapping'' of many lines of sight through a single cloud can now be performed. Comparison with [sub]millimeter spectroscopy mapping over the same region will provide a direct test of over 30 years of CO measurements. These measurements will also test recent large-scale maps of near-infrared extinction as probes of the physical structure of molecular clouds. We propose to test these ideas toward the $\rho$ Ophiuchus molecular cloud, where these results will have immediate impact upon extensive existing ground- and space- based infrared and submillimeter observations, as well as observations to come.

GS-2002A-Q-18

Title: Imaging of the Dust Torus in Proto-Planetary Nebulae

Abstract: The origin of the rich variety of morphologies observed in planetary nebulae (PNs) is one of the major unsolved problems in stellar evolution. While major progress has been made on understanding the general shaping of PNs by the interacting winds theory, it is not clear when the shaping begins. Many proto-planetary nebulae (PPNs) are found to have bipolar morphology by the HST, suggesting that shaping occurs early and over a very short time. Recent observations have suggested that PNs are shaped by a fast, collimated, outflow in the PPN phase, and such outflows are collimated by a dust/molecular torus. We propose to use the T-ReCS instrument to obtain mid-infrared images of 5 southern PPNs with the goal of determining the size and geometry of these dust torii.

GS-2002A-Q-19

Title: Quick Response to GRBs: the early burst and the late-time decay

Abstract: We propose Quick Response observations of gamma-ray burst afterglows using the Gemini South acquisition camera. The unusual combination of excellent sensitivity and rapid readout will enable unique science goals. For the smallest HETE2 error boxes (radius < 1'), we request fast searches for the counterpart, to explore the unknown early-time afterglow behavior and examine the causes of optical non-detection of many afterglows, including the elusive class of short-hard bursts. Where the afterglow is easily found, the rapid readout will allow us to search for short-term variability that could betray continued activity of a compact remnant. In the cases that an afterglow is too faint for smaller telescopes, the rapid response by Gemini will allow a dramatically deeper search than has so far been performed. We also propose late-time multi-color observations of afterglows, to search for supernova-like features in the light curves on timescales of 2-6 weeks. In conjunction with STIS spectroscopy approved in our HST Cycle 10 proposal, these observations will provide a stringent test of the hypothesis that GRBs are associated the collapse of massive stars.

GS-2002A-Q-20

Title: Mid-Infrared Imaging of Disks of Transitional Herbig Ae/Be Stars

Abstract: We propose to use T-ReCS to image at 10 and 20 microns the dusty circumstellar disks of Herbig Ae/Be stars that appear to be at an evolutionary stage between the very young embedded Herbig stars and their main sequence progeny, the so-called Vega-type stars. By choosing this special sample of "transitional" stars that are approaching the ZAMS, we will be able to explore disks that are less than a million years old and at a very early phase of planet formation. Because these particular pre-main-sequence stars have evolved beyond the heavily embedded phase, most of the excess IR emission should be associated with disks rather than placental envelopes. Nevertheless, our high-angular-resolution, diffraction-limited imaging with T-ReCS should be able to distinguish disks from any significant extended residual envelope emission. A key goal is to spatially resolve the disks or place severe limits on the sizes of the mid-IR-emitting regions, the success of which is enhanced by the proximity (<200 pc) of most of these objects. As shown previously, disk structure such as holes, gaps, and asymmetries are critical clues to the evolution of disks and planetary systems. Limits on the source sizes can constrain dust particle temperatures and sizes and provide insight into the planetary growth process and evolutionary stage of the disk.

GS-2002A-Q-21

Title: Winds in post-AGB stars: shaping planetary nebulae

Abstract: A most intriguing challenge is to understand how asymptotic giant branch (AGB) stars transform themselves in a few thousand years into the variety of shapes (spherical, elliptical, bipolar) and sizes observed in planetary nebulae. A fast stellar wind in the post-AGB phase is the most often suggested machanism for producing the transformation. We have a sample of AGB-to-PN transition candidates which show emission lines indicating the development of a fast wind. We wish to get high resolution infrared spectra of the emission lines in these objects in order to understand the development of the fast wind across the HR diagram. Such knowledge is necessary input into the modelling of the nebular asymmetries that develop during the post-AGB phase.

GS-2002A-Q-22

Title: Multiplicity and Circumstellar Structure of Deeply Embedded Herbig-Haro Energy Sources

Abstract: We propose to perform a survey of ~100 (20 in 2002A) newborn and deeply embedded sources all of which drive Herbig-Haro flows, using Gemini South and the facility mid-IR instrument, T-ReCS. The sources of Herbig-Haro jets have ages between 10^4 and 10^5 year, and are therefore among the youngest stars known. New studies suggest that jet formation may be triggered by dynamical interactions in binary or multiple young stars (Reipurth 2000). If this is correct our sample should contain a large fraction of multiple sources with many close binaries. We will compare the statistics of binarity and separation distribution with those of much more evolved T Tauri stars to study if disintegration and orbital evolution are important components of these early stages of stellar evolution. Circumstellar material/disks are abundant at such early evolutionary stages, and from the same dataset, we will study the extent, morphology and nature of such material and determine how often circumstellar disks have survived in multiple systems.

GS-2002A-Q-23

Title: Probing the forming cores of galaxy clusters

Abstract: Studies of rich clusters to z=1 indicate that galaxies in their central regions finished forming the bulk of their stars at z>2, in contrast to field galaxies, which formed half of their stars since z=2. The difference in star formation history is due to the mechanics of forming the core of a cluster at high redshift, the details of which are not clear. Key to understanding this are studies of galaxies at the centres of z>2 (proto) clusters, hampered by the fact that we have yet to discover a sample of such clusters! Blind optical, Xray and SZ surveys are several years away from generating samples of clusters at z>2. However, by targeting the environments of z>2 powerful radio loud AGN using FLAMINGOS, we aim to discover high redshift (proto) clusters and subsequently characterise the galaxy population in the forming cluster cores. NTAC time split requested for this proposal : CL=12hr, UK=16hr, AU=4hr

GS-2002A-Q-24

Title: Massive YSOs in W31

Abstract: We plan to observe candidate massive YSOs in W31 in order to derive the parameters of the embedded stars. Objects with similar characteristics: high luminosity and excess emission in the K-band have been found in other Galactic giant H II regions (e.g. M17, W42, W43, NGC3576). Some of these are coincident with ultra compact H II regions, indicating the existence of a connection between these two groups. Establishing an evolutionary sequence between the different kinds of YSOs is the first step in understanding the physical processes involved in the formation of massive stars. Since the high obscuration and veiling by intense dust emission can preclude the detection of photospheric features, we propose to observe in the mid-infrared in order to derive the parameters of the embedded stellar cores for a set of objects in W31 for which we already have near infrared data.

GS-2002A-Q-25

Title: Circumstellar H$_2$ and H$_3^+$ Line Emission in HD 141569

Abstract: Planet formation has long been known to be intimately associated with the accretion and evolution of gas and dust around disks of young stars. A comprehensive understanding of the physics and chemistry of young circumstellar disks is therefore critical to a complete picture of star and planet formation, yet basic questions about the gas content and physical processes in protoplanetary disks remain largely unanswered. Recent observations of the circumstellar disk around Herbig Ae star HD~141569 by the PI have uncovered highly-excited emission lines from CO and H$_3^+$, which must stem from circumstellar material close to the young star. We propose a highly targeted spectroscopic study of the HD~141569 system to elucidate the excitation mechanism and conditions of H$_3^+$ and H$_2$ in this disk. Such observations represent significant and timely tests of theory and exploit the unique capabilities of the Phoenix spectrometer at Gemini South.

GS-2002A-Q-26

Title: Towards an Evolutionary Sequence for Massive Star Formation

Abstract: We are proposing to undertake a population census of the massive protostellar sources within three molecular cores in the star forming complex G14.60+0.02. We will use TReCS on Gemini-S to conduct a multi-wavelength mid-IR imaging survey of these cores, to identify the sources present, estimate their luminosity and study the surrounding proto-stellar environment. This proposal builds upon extensive sub-mm and methanol maser surveys of protostellar cores, and exploratory studies at near- and mid-IR wavelengths, that we have conducted. From this work we have hypothesised an evolutionary sequence of stages through which massive star formation occurs, from cold sub-mm core, to hot molecular core, to UCHII region. The three cores in G14.60+0.02 appear to represent each of these stages, and so are suitable for examining this hypothesis in detail.

GS-2002A-Q-27

Title: The Star-Forming History of Isolated Dwarf Spheroidal Galaxies

Abstract: The dwarf spheroidal galaxies that have been most extensively studied to date are those that are in the outer halo of the Milky-Way. However, the evolution of these galaxies has likely been influenced by interactions with the Milky-Way. In order to understand the evolution of dwarf spheroidal galaxies in general and make meaningful comparisons with models it is necessary to study this type of galaxy in isolated environments as well. We propose to use Flamingos I to obtain deep J and Ks images of three nearby isolated dwarf spheroidal galaxies. One of our targets, Tucana, is on the periphery of the Local Group, and will be observed to serve as a basis for comparison with the other systems. The other systems (ESO540-030 and Scl-dE1) are located in the Sculptor group, with distances of 0.5 - 0.7 Mpc from other large galaxies. The data will be used to probe the star-forming histories of these systems based on the luminosity function of AGB stars. Moreover, these data will serve as the basis for follow-up spectroscopic observations with the same instrument when the multi-slit mode becomes available to probe the chemical composition of these galaxies. This is a re-submission of a program that was not conducted in 2001B because of problems with the instrument.

GS-2002A-Q-28

Title: Mid-Infrared Imaging of the G29.96-0.02 Hot Core

Abstract: Hot molecular cores represent the earliest observable stages of massive star formation. These sources are heavily embedded and young, and can only be observed between wavelengths of 5 microns an a few mm. Newly developed models of these hot core phases of massive star formation enable one to determine for the first time detailed physical properties of these sources, such as accretion rate and central star luminosity, from multiple wavelength observations in the mid-infrared. In May of 2001, a hot core was detected at mid-infrared wavelengths at Gemini North using OSCIR. This source, G29.96-0.02 is one of only two known mid-infrared bright hot cores. I propose to perform multiple wavelength photometry on this hot core, and through the use of the models, determine for the first time the physical properties of the earliest observable stages of a massive star.

GS-2002A-Q-29

Title: High-Resolution Imaging of Circumstellar Disks in Massive Star Forming Regions using T-ReCS

Abstract: It is not known with certainty if young massive stars have circumstellar disks. If massive stars form via accretion similar to low mass stars, the presence of such disks are expected. Due to the fact that young massive stars form in obscured regions, little is known about them. However, advances in mid-infrared astronomy now allow direct detection and observation of massive stars in the earliest stages of life from the largest ground based telescopes. Mid-infrared observations at the CTIO 4-m, we have resolved what appear to be three circumstellar disks around high mass stars. These young massive stars all exhibit methanol maser emission, which is believed to trace circumstellar disks. We propose to use T-ReCS to perform high-resolution imaging of these resolved circumstellar disks in order to study the detailed properties of the disks. We also propose to observe additional circumstellar disk candidates displaying methanol maser emission to provide further conclusive and direct proof that massive stars form via accretion and have circumstellar disks.

GS-2002A-Q-30

Title: Mid-Infrared Observations of Bright SCUBA Sources in MSX Infrared-Dark Clouds

Abstract: The MSX infrared-dark clouds (IRDCs) are dense, cold molecular clouds containing bright, compact SCUBA sources that appear to be in the early stages of star formation. We propose to use T-ReCS to observe a number of our SCUBA sources. Where MSX 8-micron emission is associated with the SCUBA sources, these observations should reveal whether they consist of single, multiple, or extended sources. Where no 8-micron emission is apparent, T-ReCS could reveal the presence of low-mass or very deeply embedded protostars.

GS-2002A-Q-31

Title: A mid-IR imaging survey of proto-planetary nebulae

Abstract: We have completed a near-IR imaging polarimetry survey of 50 proto-planetary nebulae to detect and image their circumstellar structure. We find a range of envelope geometries and that axisymmetry is already very common at this stage of evolution (before the PN phase). In a preliminary study with OSCIR on Gemini-N we obtained mid-IR imaging of 4 of the these objects. By combining the mid- and near-IR data we are building detailed models of the circumstellar envelopes (CSEs) of post-AGB stars. We propose to extend this work with a further 10 targets, using T-ReCS on Gemini-S. Details of CSE properties and how they vary across a wide sample are essential for an understanding of how axisymmetry arises in these objects and how it leads to the range of morphologies observed in PNe.

GS-2002A-Q-32

Title: Young Brown Dwarfs: Exploring the Formation Process and Physical Properties

Abstract: We propose to investigate the formation process as well as reveal the photospheric characteristics of a selected group of young brown dwarfs in the Chamaeleon I star-forming cloud. Recent results indicate a formation process for these extremely low mass objects similar to the solar mass analogues, the T Tauri stars, in which disk accretion plays a major roll. Our selected candidates are expected to be young predecessors of the recently proposed L'' and T'' spectral type dwarfs. Flamingos I H+K grims (R=1000) spectra will allow us to study the photospheres of these embedded young objects and characterize the circumstellar environment, in particular the disk accretion rate. In addition, and although our selected sample is rather small (four objects), we will be able to carry out a more meaningful comparison with the solar mass analogues, the T Tauri stars, of the formation process/es and physical properties.

GS-2002A-Q-33

Title: Number Counts of Extremely Red Galaxies to Extremely Faint Magnitudes

Abstract: Extremely Red Galaxies (ERGs) are resolved objects with R-K>6. They could be dust-enshrouded starbursts at z~1-2, or they could be passively evolving systems formed at very high redshifts (and observed at z~1-2). In either case, they play an important part in the story of galaxy formation and evolution. Currently, number counts of ERGs are limited to K<19 and likely miss the vast majority of the ERG population. We propose to constrain number counts of ERGs to K=21.5 by using a modest amount of Flamingos imaging to complement our existing, ultra-deep VLT R-band image (limiting R=30). This program has been awarded 5.5 hours in 2001B but Flamingos was not ready early enough in the semester; here we are re-requesting 5.5 hours to complete this program. Our observations will explore a hitherto unprobed region of parameter space by extending the number counts of these important galaxies to ~M*, or 2.5 magnitudes fainter than is known at present.

GS-2002A-Q-34

Title: G353.2+0.9: A laboratory for theories of star formation.

Abstract: O-type stars, during their very short life, strongly modify the surrounding interstellar medium, starting from the action of their powerful stellar winds and ionizing ratiation, and often finishing with spectacular supernova explosions, which contribute to the chemical enrichment of the interstellar medium, sometimes triggering the formation process of new generations of stars. These hot stars are also responsible for most of the ionization and dynamics of giant HII regions and starbursts, and strongly influence the Initial Mass Function (IMF) of young stellar groups. In spite of their outstanding characteristics, O-type stars are often elusive to careful studies: the beginning of their life happens in dense, highly obscured, molecular clouds, and their evolution is so fast, that by the time they blow away the surrounding dust, they are already at somewhat evolved, having lost a considerable fraction of their initial mass. More inconveniences come from the fact that the IR, optical and near-UV colors of O-type stars are degenerate, and the far UV is highly affected by extinction. We propose JHKs observations of a selected area in the galactic HII region NGC 6357. Point sources will be imaged down to Ks=18 with S/N = 10, in order to detect not only massive newborn stars but also pre-main sequence (PMS) intermediate and low mass stars. The observations will cover an area of nearly 5 x 5 arcmin centered in the nebula G353.2+0.9 whose radio, IR and optical characteristics are indicative of ongoing massive star formation. The observations will be used to derive photometric near IR magnitudes and colours of stellar sources and to study the morphology of the region. Our aim is to detect IR sources corresponding to newborn massive stars, to analyse the traces of their interaction with the surrounding nebula and its influence in the formation of lower mass stars. This project has been granted 3 hours in semester 2001B service observing for Gemini South. Unfortunately, instrumental problems imposed a delay in the Flamingos queue, starting operations when our targets were already unreachable.

GS-2002A-Q-35

Title: Probing the forming cores of galaxy clusters

Abstract: Studies of rich clusters to z=1 indicate that galaxies in their central regions finished forming the bulk of their stars at z>2, in contrast to field galaxies, which formed half of their stars since z=2. The difference in star formation history is due to the mechanics of forming the core of a cluster at high redshift, the details of which are not clear. Key to understanding this are studies of the galaxies at the centres of z>2 (proto) clusters, hampered by the fact that we have yet to discover a sample of such clusters! Blind optical, Xray and SZ surveys are several years away from generating samples of clusters at z>2. However, by targeting the environments of z>2 powerful radio loud AGN using FLAMINGOS, we aim to discover high redshift (proto) clusters that surround them and subsequently characterise the galaxy population in the forming cluster cores. We request time split 16:12:4 UK:CL:AU.

GS-2002A-Q-36

Title: Isotopic ratios and physical conditions from the hyperfine structure and broadening of IR coronal lines in PN NGC6302

Abstract: NGC 6302 is a very high excitation Planetary Nebula (PN) with emission from a broad range of ionisation stages, up to [SiIX]~3.94um. A filled-in structure and small expansion velocities in an obscured core represent a unique astrophysical situation in which to: 1- look for hyperfine shifts in infrared coronal lines, and thereby measure isotopic ratios and probe s-processing in NGC~6302's progenitor 2- improve our understanding of photoionised nebulae by using the information in the emission line profiles. Phoenix on Gemini South allows performing R~75000 spectroscopy of selected near-IR lines.

GS-2002A-Q-37

Title: Post-starburst QSOs: spatially resolving the missing link.

Abstract: We propose to use NIRI to image a sample of post-starburst QSOs selected from the 2dF QSO Redshift Survey. These objects show the broad emission lines typical of QSOs but also show a significant Balmer break and the strong Balmer absorption features typical of post-starburst populations of age <1Gyr. Post-starburst QSOs provide a unique opportunity to study the link between AGN activity and star formation. They are potentially the evolutionary link between ultra-luminous infrared galaxies and normal QSOs. A detailed morphological study of such sources, using the high spatial resolution available in the IR with Gemini, allows us to determine the location of the starburst relative to the AGN component on kpc scales. In particular we wish to determine if the majority of the starburst flux is coincident with the AGN, or more extended. We also aim to search for evidence of galaxy interactions and mergers. These post-starburst QSOs provide an opportunity for us to test the supposed connection between star formation, AGN activity and galaxy mergers/interactions.

GS-2002A-Q-38

Title: Reverberation Mapping of Black Hole X-ray Transients

Abstract: Reverberation mapping has been widely used to explore the broad-line region of AGN, but has only recently been effectively applied to X-ray binaries. This reflects the shorter delay timescales involved, of order seconds, which require demanding time resolutions. We will use the large collecting area of Gemini-South together with the rapid readout of the Acquisition Camera to build on our existing progress in this field. We will perform Quick Response X-ray to optical reverberation mapping on a black hole X-ray transient in outburst with X-ray flux >1 Crab and/or V<14. We will probe the structure of the accretion flow, identifying reprocessing sites (the accretion disc, the heated companion star or both) and exploring the structure of the irradiated disc. These observations will form part of our existing, successful multiwavelength programme, and will be coordinated with our approved RXTE observations.

GS-2002A-Q-39

Title: White Dwarf Seismology in M4

Abstract: We propose to use the Acquisition Camera on Gemini South to obtain accurate time series photometric data for a potential variable DB (helium-rich) white dwarf star in the Galactic Globular Cluster (GGC) M4. The target star, which was discovered in a deep HST M4 imaging project (Richer et al. 1997), is both bright and isolated from nearby stars. The magnitudes and colours of the star are consistent within the location of the extended instability strip for DB pulsating stars. In addition to providing fundamental constraints on pulsation models and atmospheric models of white dwarfs, the detection and measurement of a variable white dwarf in a GGC would provide crucial information regarding stellar evolution through nuclear cross sections for certain reactions. Given the short period of the expected variability (~10 minutes), accurate time series data is required with an instrument that possesses a short read-out time. The target magnitude (B = 21.8) also requires a large aperture telescope to obtain a decent signal-to-noise in many individual short exposures. The Acquisition Camera on Gemini South is an ideal instrument to obtain these measurements.

GS-2002A-Q-40

Title: Mid-infrared Imaging of Southern Bipolar Reflection Nebulae

Abstract: We propose to obtain mid-infrared images of 5 reflection nebulae with bipolar structures and cool central stars. The mid-infrared images are expected to reveal the "dark" dust torus around the waist of the bipolar lobes. By overlaying these images with the optical images from the HST, we will obtain a more complete picture of the mass distribution for a better understanding of the nature of these peculiar objects.

GS-2002A-Q-41

Title: Searching for the Bottom of the Initial Mass Function

Abstract: The minimum mass of the Initial Mass Function (IMF) should be a strong function of the physical processes that dominate in the formation of stars and brown dwarfs. To date, the IMF has been measured down to $\sim10$~$M_{\rm Jup}$ in star forming clusters; there is no sign of a low-mass cutoff in the data for these clusters. To determine the lowest mass at which objects can form in isolation in a typical star forming cluster, we propose to use FLAMINGOS on Gemini South to obtain deep $JHK_s$ images ($H=20$) of the Chamaeleon~I cluster (1~Myr, 160~pc). By combining these data with very deep photometry from $HST$ and $SIRTF$ (0.8, 0.9, 3.6, 4.5, 5.8, 8.0~\micron), we will search for young brown dwarfs in Chamaeleon~I down to masses of $\sim1$~$M_{\rm Jup}$.

GS-2002A-Q-42

Title: Survey of the Circumstellar Environments of Prolific Wolf-Rayet Dust Makers with T-ReCS

Abstract: We propose to extend our survey which successfully started with OSCIR/Gemini-North in 2001, this time using the high angular resolution and sensitivity of T-ReCS/Gemini-South to resolve and map the coolest regions of dust envelopes around known prolific dust-making, population I Wolf-Rayet (WR) stars. The high resolution, 3-color images of 4 IR-bright and presumably extended WR sources will broaden and reinforce the important conclusions derived from the analysis of the unique system WR 112. Namely, they will help (I) to better understand the physics of dust survival in apparently hostile, hot-star environments, backing our estimate of the dust destruction rate in the binary system WR 112, studied already with OSCIR/Gemini-North; (II) to verify and fine-tune models of dust formation by supplying practically model-independent information about (a) the chemical composition and characteristic size of the dust grains, (b) the temperature profile in the dust envelope, and (c) the dust formation rate.

GS-2002A-Q-43

Title: Hidden Star-Formation in Low-Metallicity Galaxies

Abstract: We propose to observe with T-ReCs on Gemini the galaxy Mrk1236. This galaxy shows an intriguing radio source with a rising continuum, proposed to be produced by an embedded super-star cluster. We want to test this hypothesis by looking in the mid-infrared, where the optical depth is low enough to detect the presence of hidden star-formation. The confirmation and quantification of the presence of massive stars not visible in the optical in low-metallicity system is a key point in the determination of the star-formation rate in the young Universe.

GS-2002A-Q-44

Title: A CO Resonance Scattering Map of alpha Ori's Circumstellar Shell

Abstract: The detailed mass-loss mechanism for late-type stars is still unknown after several decades of studies. One way to explore this further is to map the inner wind regions around these stars. We propose to use the unique Phoenix-Gemini combination to do this. Microwave emission lines and optical resonance lines have been used to image circumstellar shells on the sky. A new technique recently exploited by us is to image resonance scattering from infrared vibration-rotational carbon monoxide lines. This technique explores the inner shell region providing complementary information to other techniques. Infrared CO mapping is especially powerful since extraction of excitation temperature and column densities is possible. Information on the velocity structure and the development of clumps in the flow will be extracted. The present proposal focuses on the study of the shells around Betelgeuse ($\alpha$ Orionis).

GS-2002A-Q-45

Title: IR Detection of Low-Mass Secondaries in PMS Spectroscopic Binaries

Abstract: We propose {\it Phoenix} observations of 4 pre-main sequence single-lined spectroscopic binaries in Orion, and HD 98800 A and B, in the TW Hydra association, in order to detect the companions in these systems. Our dynamical measurement of the mass ratios will provide input to theories of binary star formation and circumstellar disk evolution, and represent the first step toward eventual measurement of the component masses.

GS-2002A-Q-46

Title: IR Detection of Low-Mass Secondaries in PMS Spectroscopic Binaries

Abstract: We propose {\it Phoenix} observations of 4 pre-main sequence single-lined spectroscopic binaries in Orion, and HD 98800 A and B, in the TW Hydra association, in order to detect the companions in these systems. Our dynamical measurement of the mass ratios will provide input to theories of binary star formation and circumstellar disk evolution, and represent the first step toward eventual measurement of the component masses.

GS-2002A-Q-47

Title: Detection and Measurement of Ions Winds on Uranus

Abstract: We propose to make a study of ionospheric winds on Uranus, measuring Doppler shifts in the H3+ R(1,0) line with the Phoenix spectrometer, a visiting instrument on Gemini South. Such observations are particularly timely because the Uranian magnetic pole can currently spin onto the noon meridian, so that it directly faces into the Sun. This allows the solar wind to penetrate straight into the ionosphere, and with the Solar Cycle at a 11-year maximum, produce very powerful auroral effects. Our observations build on previous experience with Jupiter, and by analysing the wind velocities across the central meridian, we expect to be able to detect the location of the magnetic pole, the associated aurora, and the wind system produced therein. Our view of this system will allow us to extrapolate our results out to investigate ionospheric/magnetospheric interactions, and thus provide a new map of the configuration of the Uranian magnetosphere.

GS-2002A-Q-48

Title: Mapping the Dust and UIR emisison in Planetary Nebulae

Abstract: While it is generally assumed that the dust in planetary nebulae represents remnants of circumstellar dust envelopes ejected during the preceeding asymptotic giant branch phase, there has been no good mapping of the dust distribution in planetary nebulae. Recent ISO observations have found aromatic hydrocarbon band (AHB) emission and cystalline silicate features in many planetary nebulae. We propose to use TReCS to map a number of planetary nebulae in the 11.7, 12.5, 18.3, and 24.5 micron filters to isolate the emission region of the AHB features and in the 18.3 and 24.5 filters to isolate the crystalline silicate feature. These observations will allow us to trace the formation history of these species.

GS-2002A-Q-49

Title: Nucleosynthesis in Massive AGB Stars

Abstract: Massive AGB stars (3-8 M_sun) make a substantial contribution to the enrichment of the interstellar medium in many elements and isotopes such as 4He, 7Li, 12,13C, 14,15N, 16,17,18O, 22Ne, 26,27Al, 24,25,26Mg and s-process elements. However, at the present time, theoretical models for the production of these elements by helium shell flashes and hot-bottom burning are highly uncertain, largely because of our inability to reliably treat stellar convection. Here we aim to get observational determinations of element abundances in highly-evolved massive AGB stars in order to test models.

GS-2002A-Q-50

Title: TRECS Imagery of Circumstellar Disks: Herbig Ae Stars

Abstract: Analysis of the spatial distribution of dust (carbonaceous/siliceous species) and silicate mineralogy (crystalline/amorphous) of pre-main sequence Herbig Ae stars probes the chemical and physical conditions in these potentially planet-forming environments, the condensation of dust from the gas-disk, and/or the processing of grains. We propose to obtain spatially resolved, narrow-band T-RECS imagery of four nearby ($\leq 240$ pc), young ($\leq 6$ Myr) Herbig Ae stars to: (1) spatially resolve putative proto-planetary disks, (2) determine the grain properties in the centrally concentrated versus spatially extended dust species (e.g., silicates versus PAHs), and (3) assess the presence of close companions. The diffraction limited image quality of GEMINI-S (+T-RECS) at 10~\micron \ will enable study of the environment within $\leq 100$~AU from the central star. The spatially resolved imagery is crucial to unambiguously determine the disk + disk envelope geometry.

Last update January 15, 2002; Phil Puxley