Here we present, in short, few projects among the wide variety that can be studied with OSIRIS, from solar system to extragalactic astronomy. Some key projects are being studying by the scientific team for a best exploitation of the instrument at the GTC.
Asteroids and Comets
Broad-band photometry in the optical has been a classical technique for decades to classify asteroids based on their reflectance and also study properties such as their morphologies, spottiness of their surfaces and rotation periods. Its combination with low-intermediate resolution spectroscopy has also proved to be useful in the determination of their compositions. Unfortunately, this information is only available for the intrinsically brightest or nearest of them, and a research needs urgently to be conducted on the smaller size bodies and also Kuiper Belt objects (Trans-Neptunian). Their study using both observational techniques in combination with a large-diameter telescope would be very important in the determination of the planetary formation stage in the solar system, as well as the origin of the small diameter objects. Comet research would also benefit from the possibility of simultaneous photometry and spectroscopy (another case for parallel observations) since it is still not quite clear currently the radial behavior of the different molecular spices ejected from the nucleus, the role of dust and also the mechanisms regulating the formation of the tails.
Variable stars
Time-series observations of binary stars in emission lines (CaII H and K, CaII triplet, Balmer Ha , Hb ,...) and photometric minima (due, presumably, to spots) would allow to pin down the origin of the observed activity. These objects are highly variable in short time scales. Then, time series using OSIRIS with TF and charge shuffling will be very suited.
Stellar activity cycles in open cluster stars
The TF and charge shuffling option on OSIRIS will make it possible to obtain on- and off-band K-line images of cluster stars, and thereby monitor stellar activity in stars all along the main sequences of clusters of all ages. Some work is being done at the WIYN telescope with multi-fiber spectroscopy, but it is slow and a relavitely small number of stars can be followed. With OSIRIS, one could monitor an entire cluster regularly, taking probably less than an hour in any one night. Activity levels, and potentially even rotation periods, could be found.
Stellar populations in remote parts of the galaxy
With broad-band photometry, and the large field of view and aperture available to OSIRIS, it will be possible to study the stellar populations -ages and compositions- of stars in the furthest parts of our galaxy. In particular, there are some small windows directly in the galactic plane, through which one can actually see galaxies. With OSIRIS in an imaging mode it would be possible to map the distribution of ages and compositions of stars right through to the edge of the galaxy.
Brown dwarfs
Brown dwarfs
candidates can be searched by broad band imaging multicolor
photometry, and its surface temperature confirmed via low-resolution
optical spectroscopy.
White dwarfs in star clusters
There have been some searches for white dwarfs in clusters using HST, but the field of view of the telescope is just too small, and the aperture is too small for spectroscopy of the fainter ones. With low-resolution multi-object spectroscopy, OSIRIS could identify the white dwarfs in a cluster and separate them from background dwarf blue galaxies, etc. Then one could characterize the white dwarf populations of clusters as a function of age. It would be possible for the first time to really define the cooling sequences of white dwarfs using stars of known age.
HII Regions in Galaxies
The instrument can be used for the determination of the physical properties (temperatures, densities, metallicities, etc) of every HII region in a sample of spiral galaxies in order to detect not only possible radial gradients of these properties, but azimuthal ones, due to spiral arms. For this purpose, OSIRIS could be used together with TFs and charge shuffling.
Black Hole Hunting
Recent observations of nearby galaxies have suggested the possibility that supermassive Black Holes, BH, exist at the centers of most of them if not all. Although the number of objects with solid detection are still a few tens, a tendency for the mass of the central BH to scale with the luminosity of the bulges of the host galaxies seems to be suggested by the data. To test this correlation, together with the universality of BH at the centers of galaxies, and their relation with the onset of the different kinds of nuclear activities seen in galaxies, it is essential to use large-diameter telescopes in combination with deep photometry (to determine the mass-to-light ratio curves inwards into the bulge) and spectroscopy of intermediate-high resolution (to determine the stellar velocity dispersions). The same techniques can be used for galactic BH candidates, as has been successfully proved with V404 Cyg.
Surveys of galaxies
Both active and quiet versus z, studying its morphology and photometric properties. 10m-class telescopes are able to reach higher z than now in this classical field of work. This kind of studies would provide data on galaxy evolution, the origin of the nuclear activity and the reason of the lack of nearby QSO.
AGN-Normal galaxies link
10m-class telescopes will allow to observe normal galaxies at high redshifts, but the relation between AGNs and normal galaxies would be still crucial to understand galaxy evolution. The fraction of galaxies that has an active nucleus is still an unanswered question. It would be necessary to have spectra of statistically significative samples of galaxies. 8-10m-class telescopes with multiobject spectroscopy facilities are needed to undertake observations at z>2. Deep imaging and spectroscopy surveys of AGNs, excluding QSO (such as Seyfert galaxies, for example) at redshifts higher than that observed today (which then requires low-resolution spectroscopy), would probably yield new surprises to the actual scenario.
AGN Unification Models
It is widely accepted that AGN unification based on orientation effects is valid up to a certain extend. Some aspects of the scenario are still unclear. For example, how universal is the unification? There AGN that depart from the standard unification model. This problem can be solved with narrow band direct imaging of complete AGN samples of different types in order to analyze the ionization cones and the hidden AGN nuclei. But, again, large-class telescopes are needed to extend the results to z>2. Another question is the unification of radiosources and radio quiet objects. To study this issue spectroscopic observations (to elucidate the nuclear kinematics) and high-resolution imaging are needed.
AGN components
The NLR extends from a few pc up to hundreds of pc and its modeling provides unique information on the physical properties of the interstellar medium of the host galaxy at these scales. The NLR can be studied from UV through the FIR and, together with spectroscopy, the more powerful technique is narrow band direct imaging of emission lines. Also, the study of the continuum ionizing radiation pattern would allow to distinguish among the different models of the nuclear continuum. Also, the high spatial resolution (0.125 arcsec/pixel) of OSIRIS, along with the excellent expected seeing of GTC will allow an accurate deconvolution of the nuclear component of active galaxies. This will help to determine the physical characteristics of AGN nuclei, including their spatial scale, thus allowing to test the AGN standard model versus alternative hypotesis.
Optical counterparts of radiojets
Except a few cases at the beginning of HST observations (pre-COSTAR), no other optical counterpart of radiojets has been detected. Expected surface brightness magnitudes are of the order of 27th-28th in V, which requires telescopes larger than the HST. On the contrary, a good camera with good sampling (~0.125 arcsec/pix) in a 10m Earth-based telescope can be successful. Then OSIRIS is ideally suited for the task.
Optical counterparts of GRBs
This instrument will be able to detect and follow up to very faint magnitudes optical counterparts of Gamma Ray Bursts. Optical counterparts detected up to now can have R magnitudes larger than 20th, with a very steep fading (more than one magnitude per day), but constant color.
The Origin of the X-ray Background
It has become increasingly clear that obscured AGN may be the source of the X-ray background. Current predictions suggest that there will be a source density of 5000 objects deg^-2 at R < 25mag. Most of these objects will have narrow emission lines in the optical region, red optical-to-near IR colours with possibly broad emission lines in the near IR. The next generation of X-ray satellites (e.g. AXAF) will be able to pinpoint these X-ray sources with arcsecond accuracy. The larger field-of-view available with OSIRIS is therefore ideally suited to the follow-up imaging/spectroscopy of these sources, with the proposed wide wavelength coverage (particularly into the near-IR) being well suited to determining the underlying nature of these objects.
QSOs
QSOs are the brightest objects in the Universe and the only ones that provide information about the high redshift Universe. The study of the QLF is of primordial importance to understand the processes that control the central AGN and to study the large scale structure of the Universe. The QLF behavior can be considered established at redshifts below 2.2. Beyond this redshift the scenario is less clear. Multicolor techniques can be used to select QSOs up to 25th-26th V magnitudes, and then, using VRI photometry, reach high redshifts. An instrument like OSIRIS in a 10m-class telescope can be ideal for this kind of studies, because magnitudes never reached before in QSO surveys can be achieved.
The Environments of QSO at z>1
Large-scale QSO redshift surveys (2dF, Sloane) will be an important cosmological tool in the early years of the 21st century. However, in order to relate large-scale structure determined from QSOs to that derived from galaxies, the relationship between QSOs and galaxies needs to be determined. The most direct way to establish this is to observe the galaxy environments of QSOs, yet there is little or no data at z>1. OSIRIS is ideally suited to extending this work to z=2 through TF imaging at the wavelength of redshifted [OII]. Projects including matched samples of radio-loud and radio-quiet AGN would provide a unique data-set to establishing the relationship between QSOs and galaxies, and would also provide an important.
Clustering around radio sources
Nearby (z<1) radio sources are, in general, located in the center of galaxy clusters, and it is assumed that this fact could be determinant in the origin of the radio activity and in the subsequent evolution of the radiosource as well. However, the identification of clusters of galaxies surrounding far radio sources is scarce, mainly because its low brightness. While the radiogalaxy or radio QSO the brightest object of the cluster, the rest of the cluster members can be two or more magnitudes fainter. The study of high z clusters is a very powerful tool, not only to answer questions related with the radio emission origin, but also to study the evolution of the Universe. The instant of the formation of large structures (such as clusters) is important to test cosmological models. To be able to detect this clusters, it is fundamental to obtain very deep images of wide fields, because they can extend up to tens of arcmin (at z~3-4) and the galaxies that constitute them can be as faint as 26th-27th magnitude. Also a complete study would require multiwavelength observations to determine if a given galaxy belongs to the cluster or not, and to study its colors. Low-resolution spectroscopy of the largest possible number of galaxies of the cluster would complete the study. This is a clear case where a 10m-class telescope is fundamental and where the HST is not a convenient tool. This issue could be tackled efficiently by OSIRIS.
Evolution of low-redshift galaxies
Multi-object spectroscopy of faint galaxies in the range z=0-2, would be very useful to study the evolution of physical properties of galaxy populations.
Determination of redshifts of faint objects
TFs will be very useful to make photometric redshifts surveys of very faint objects. The optical domain allows to explore the range z<1, and the TFs would allow accuracy higher than that achievable now with broad band conventional techniques (dz~0.2). The low-resolution spectroscopic capabilities of OSIRIS will complement this issue to determine redshifts for given objects or clusters.
Probing Dark Matter
Low-resolution spectroscopy with a 10m-class telescope allows to study damped Lya systems which provide constraints for dark matter scenarios.
Microlensing
Apart from the traditional photometric monitoring programs already being carried out towards the bulge of the Milky way and LMC, the incorporation of simultaneous spectroscopy would allow the determination of the spectral properties of the objects candidate for gravitational lenses and therefore definitively prove its stellar nature (still an open question).
Last update July 12, 2005, by Héctor Castañeda