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Sci TR-42

Updates: 14.05.2012 (Aliş, Aybüke)

4.2 Optical

TUG (TUBITAK National Observatory)

TUG is the only national observatory of Turkey which currently hosts RTT150 (1.5 m telescope) as the largest telescope. The observatory plans to have a larger one in the near future. DAG project can create synergy with TUG especially in the context of making simultaneous observations in different wavelengths or with different techniques such as imaging can be done at TUG whereas spectroscopy at DAG. The most likely science topics that will benefit from such a synergy are transient phenomenons. In the case of TUG having a larger telescope, exchanging observing runs or conducting complementary observations can be done especially if the weather conditions are considered.

VLT Survey Telescope (VST)

VST is a 2.6-m telescope installed at Paranal, Chile. It is equipped with a 268-megapixel camera called OmegaCAM with a total FoV of 1 degree x1 degree. VST is dedicated to survey programmes that have started in 2011:

  • The Kilo-Degree Survey (KIDS) - PI Konrad Kuijken (Leiden)
    This survey aims to image 1500 square degrees in 4 bands (to be complemented in the near-infrared with data from the VIKING survey). The survey aims to cover this large area to a depth 2.5 magnitudes deeper than the Sloan Digital Sky Survey (SDSS), with considerably better image quality. The primary science driver for the design of this project has been weak gravitational lensing. The science goals of the KIDS project are numerous, including: studying dark matter halos and dark energy with weak lensing, investigating galaxy evolution, searching for galaxy clusters, and looking for high redshift quasars. The KIDS project fills an important niche in lensing surveys between smaller, slightly deeper surveys, such as the CFHT Legacy Survey, and larger, shallower surveys like the SDSS.
  • The VST ATLAS - (PI: Tom Shanks; Durham)
    This survey is targeting 4500 square degrees of the Southern Sky in 5 filters to depths comparable to the SDSS. This survey will also be complemented with near-infrared data from the VHS VISTA survey. The primary science driver is to determine the dark energy equation of state by examining the 'baryon wiggles' in the matter power spectrum, via surveys of luminous red galaxies using both photometric and spectroscopic redshifts. But this survey will also provide the imaging base for many other future spectroscopic surveys, both at the VLT and also via wide-field fibre spectrographs such as the new AAOmega instrument at the Anglo-Australian Observatory. For example, the VST ATLAS will be valuable in the hunt for high redshift galaxies and quasars.
  • VPHAS+ - The VST Photometric H-α Survey of the Southern Galactic Plane (PI: Janet Drew (Imperial))
    This survey will combine H-α and broadband u'g'r'i' imaging over an area of 1800 square degrees capturing the whole of the Southern Galactic Plane within the latitude range |b| < 5 degrees. VPHAS+ will facilitate detailed extinction mapping of the Galactic Plane, and can be used to map the structure of the Galactic disk and its star formation history. The survey will yield a catalogue of around 500 million objects, which will include greatly enhanced samples of rare evolved massive stars, Be stars, Herbig and T Tau stars, post-AGB stars, compact nebulae, white dwarfs and interacting binaries. This survey is complementary to IPHAS, a survey of the Northern Galactic Plane nearing completion, but VPHAS+ will include more filters and will achieve better image quality.

DES (Dark Energy Survey)

Currently ongoing the Dark Energy Survey is done in the southern hemisphere using CTIO's 4m Blanco telescope. It can be a very good opportunity to complete DES in the north. It should not necessarily be complementary but a way to contribute DES project can be implemented. IR plays a very important role in the high redshift regime.

DES will be complemented by VISTA in the southern hemisphere, similarly SDSS can be complemented with DAG in the northern hemisphere (especially for declinations > 60 degrees) especially after UKIRT ceases its operations.

Follow-up to EUCLID - (Red Book)

ESA approved the space mission EUCLID to fly. If everything goes with the schedule it will be launched in 2019. This is the most important thing that DAG project can contribute. EUCLID will observe galaxy clusters to obtain mass density parameter of the universe and that way the geometry of the universe can be constrained. Moreover many interesting individual clusters will be detected with EUCLID to study internal physics of clusters besides cosmological purposes. At the point of making follow-up studies DAG may play an important role in the EUCLID era.

The mission will investigate the distance- redshift relationship (galaxies and clusters of galaxies out to z~2) and the evolution of cosmic structures in 6 years life-time. It will cover 15 000 deg² in a wide extragalactic survey by 1.2 m korsch telescope, plus a deep survey covering an area of 40 deg². Field-of-View is ~0.5 square degrees in VIS (Visual imaging) and ~0.6 in NISP (NIR photometry and spectroscopy). It will be launched around 2019.

Follow-up to CFHTLS

CFHTLS has completed in an area totally 174 sq. degrees. Follow-up studies to complete the survey in the IR domain has just started using WIRCAM attached to the CFHT. But so far only Deep Survey of the CFHTLS has been approved which is 4 sq. degree. If CFHTLS-Wide will stay untouched in the IR, DAG may contribute as well. But this has less priority than the first two items above.

Updates: 11.05.2012 (Aliş)


GAIA is an ambitious mission imaging 1 billion stars, millions of galaxies, quasar, planets and focusing on average 70 times to each object in 5 years by using two different types of telescope systems and a very big CCD.

  • Science: the Milky Way, extrasolar planetary, brown dwarfs, astroids, exploding stars, general relativity
  • Astrometry: accurate measurements, even in densely populated sky regions of up to 3 million stars/deg2
  • Photometry: continuous spectra in the band 320-1000 nm for astrophysics and chromaticity calibration of the astrometry
  • Spectrometry: high resolution, grating, narrow band: 847-874 nm

GAIA will have two "photometers" the blue photometer will be sensitive to 320-660nm whereas the Red Photometer will be sensistive to 650-1000nm.

The survev will cover a magnitude range of 6 < V < 20 mag. with about 109 objects. However only down to the 15th mag the positional accuray will be 10-25 µarcsec. It will be able to measure radial velocity of stars with V < 16-17 mag using the spectrometer with a resolution of 15km/s.

GAIA should be one of the ultimate targets for a 4m telescope to perform followup observations.

  • It will be a unique mission however it will need near-IR coverage at areas where the optical extinction will be significant. If you think of it it will be able to detect an object at 15th mag with zero extinction. However if the source is in a location where there is 5 mag optical extinction that it will only be barely detected, whereas in K band the extinction will be only 0.5 mag.
  • It will need radial velocity measurements for faint stars.
  • It will be detecting a number of RR Lyrae variables etc. but the cadence of those observations will be very low hence further follow-up observations will be necessary to to be able to observe these stars (determine the periods etc.). These observations will allow for an independent determination the reddening and their distances (see e.g. Kunder et al. 2010), which will complement the parallax measurements.
  • It will also detect a number of transient events a 4m class telescope may be able to perform real good follow-up observations of these events as the GAIA will not be a pointing satellite.
  • Finally note that all of the advertised properties of GAIA are the values at the end of the mission, which is planned to be 2020. Before that everything will be much lower. For example spectrum of an F3 giant V=16 mag no extinction will have a S/N of 7 in a single measurement only when you add all of the spectra you obtain for the same star during the whole mission you will have a S/N of 130.


Kunder et al. 2010

What can be done with DAG
  • Some time can be allocated to detect type Ia supernovae.
  • Observing individual clusters using MOS type spectrographs leads reliable mass determinations and gives dynamical status of the clusters.
  • Follow-up CFHTLS in the NIR domain to complete the dataset obtained in the optical already.