Approved Science Verification Observations

The following are the observations approved by ESO's Director Generaland executed during the Science Verification phase of UT1. For moreinformation concerning these observations as well as their technicaland operational implications, please refer to the paper published inthe ESO Messenger (gzippedpostscript file).

Photometric Redshift in the HDF South

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The HDF-S will be optimally observable in late August, and certainlythis field will attract a great deal of follow-up work both from groundand space in the next few years. The SV plan is to observe the STISfield containing the quasar at redshift z=2.54 and the two NICMOSfields. Deep imaging of the NICMOS fields in UBVRI will complementthe near-IR HST data. The quasar will be observed in a narrow-bandwhich isolates objects emitting in Ly-alpha at the QSO redshift to lookfor companion objects. This will also select candidate objects forspectroscopic redshift observations with FORS1. With somewhat lowerpriority one of the WFPC2 fields may also be observed with the SUSI2set of intermediate band filters.
For more details please see the ESO HDF-South Project page.

Detection of the Gravitational Lens Responsible for the Multiply-Imaged QSOs

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The photon collecting power of the VLT can detect very faintsurface-brightness galaxies. The plate scale of the test camera shouldfurther provide very good point spread functions for the subtraction ofthe quasar images. The image quality of the VLT can be readilydemonstrated with such observations. The luminosity profiles of thelensing galaxies are fundamental input parameters for the modeling ofthe lenses.

In order to confirm the presence of the lens, a sequence of co-added VLT Test Camera images, together with the application of powerful deconvolution algorithms, should push the detection limits to considerably faintermagnitudes.

A promising object in this category is the optical Einstein ring.The faint surface brightness of this object could be suitably tested.

High-z cluster candidates

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Mass concentrations can be detected by the effects they have on thelight travel through potential wells. An easy way to identify massiveclusters of galaxies are the distorted images of background objects.The ESO Imaging Survey will provide a list of candidate clusters. X-rayselected candidate clusters will also be targeted. Detailed andsystematic studies (redshifts, structure, galaxy populations,gravitational shear maps, strongly lensed background galaxies at veryhigh redshift, etc.) will certainly form a major set of early VLTprojects. Observations in two colors (V and I) will detect and clearlydefine the elliptical galaxy sequence in the color-magnitude diagram.The field of view of the VLT-TC is well matched to the expected size ofhigh redshift clusters (~ 30" at z ~ 1). In excellent seeingconditions it should be possible to obtain high S/N shear maps, anddetect very high redshift arcs, if present.

Gamma Ray Bursters

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The optical detection of Gamma Ray Bursters (GRBs) has opened a newwindow onto these enigmatic objects. The spectral confirmation of thehigh-redshift nature of some of these events has been demonstrated.Still, not all GRBs are detected in the optical and their associationwith distant galaxies has not been shown in every case. Only a smallnumber (< 5) GRBs have been actually detected in the optical.Statistics of the gamma-ray and optical emission will build up veryslowly. Deep imaging will provide stronger limits on the opticalbrightness distribution of the host galaxies of GRBs, if present. Aproblem with the hosts of GRBs has been their relative faintness. Thethree cases investigated so far show sub-luminous (< L*) objects, whichmay rule out very massive stars as progenitors of GRBs. Imaging ofsites of optically identified GRBs could provide more information onthis issue. Should there be a GRB alert during SV with an error boxnot exceeding the field of view of the VLT-TC, we would certainlyattempt an identification.

Should Nature be kind enough to provide an optical GRB identificationduring SV we will observe its afterglow. The imaging of a former GRBsite, is not a problem. Imaging of former sites of GRBs will alsoprepare the spectroscopic observations by FORS1.

UV Imaging of Globular Cluster Cores

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One of the most intriguing, yet most interesting aspects of globularcluster dynamics is the fate of these systems after core collapse.While it is today demonstrated, on solid theoretical grounds, that theyall must undergo this catastrophic phase on a timescale of order ~10Gyr, it is still not at all clear how the stellar population in theircores would react to strong densities (up to ~ 1 billion Mo per cubicparsec) such as those expected to accompany the gravothermalinstability. Coupled with the relatively low velocity dispersion of thestars in the core, such an extremely high density sets the idealconditions for the formation of hard binaries, which will eventuallyheat the cluster core. Close binary systems and cataclismic variablesare, therefore, expected to play a dominant role in the post-collapseevolution of clusters, and should populate in large amounts the densestcores which are at higher risk of collapse.

Although only a few cataclysmic binary systems have so far beendetected in globular clusters from the ground, a random and sporadicsearch for blue variable objects in globular clusters cores conductedwith the Faint Object Camera on board the HST has already turned upquite a good number of interacting binaries. While no ground-basedinstrument can achieve the spatial resolution needed to peer deep intothe cores of dense clusters, the enormous collecting area of the VLTand the good near-UV sensitivity of the VLT-TC, coupled with theastrometric information of the available HST data, can serve this jobat best by allowing us to locate all the variables in the cores andto obtain a good light curve of the objects having a period in the2-10 hr range as might be expected from most interacting and eclipsingsystems. We will then be able to evaluate observationally the influenceof these binaries on the dynamical evolution of the clusters.

Timing of Pulsars

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The first pulsar detected in gamma rays Geminga (PSR J0633+1746) is oneof the most mysterious objects in the sky. Its parallax and propermotion have been measured and its luminosity has been obtained atvarious wavelengths. It carries all signatures of an isolated coolingneutron star. The period derivative measured in the gamma rays suggestsan age of about 340,000 years, typical of a fairly settled object.Geminga has been observed as a faint optical source at B ~ 26.5, but nopulses have been detected due to its faintness. Recently, opticalpulses have been reported from this object. Already five pulsars havedata on optical pulses all with photon counting devices. The VLT-TCshould be able to detect the optical pulses of some of these objects aswell. The pulse measurement can be achieved by repeated integrationswhile moving the charge on the CCD. Since the pulse period is knownvery accurately from observations at other wavelengths, we can move theimage on the CCD at this period and detect the pulse shape and anythermal, inter-pulse emission.

Trans Neptunian Objects

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The current inventory of the outer Solar System includes about 50Trans-Neptunian objects (TNOs), whose orbit semi-major axis is in the30-45 AU range, 7 Centaurs, orbiting between Saturn and Neptune, andmany Short-Period and Long Period Comets (SP and LP resp., a fewhundred in total).

The dynamical studies and theoretical models of these populations linktheir formation to different regions of the Solar System: while the LPcomets were formed in the Jupiter-Saturn region, then ejected by theseplanets to the outer Solar System, forming the Oort Cloud(s), the SPcomet would have formed in-situ, together with the TNOs, in 30-150 AUecliptic region, forming the Kuiper Belt. The scattering of some ofthese comets and TNOs by the planets caused them to migrate on tolarger orbits. The outward migration of Neptune caused its accompanyingorbital resonance to sweep a broad region of the inner Kuiper belt, andexplains the observed eccentricity distribution of the observed TNOs.The major problem is that these models need observational support: formost of the TNOs discovered, the only magnitude available is a crudeestimate made from the discovery image, and only a few have colormeasurements. About a dozen of short period comets and a couple of theCentaurs have been measured.

With projected proper motions in the range of a few arcsec per hour andmagnitudes around V ~ 23 - 26 for a typical TNO, several shortexposures will have to be collected for each object in order tominimize tracking problems. Candidates are available around theecliptic, however, there is a concentration near 0 hours and 12 hoursof RA due to selection effects (low star density).