Content:

• Status
• SARG Commissioning Results
  • Radial Velocities Precision (star: Tau Cet)
  • 51 Peg Radial Velocity Curve
  • Instrumental IPs
• First Results of the SARG Exo-Planets Search

Status 

Updated to: 2001/07/23

The final sample of the survey is being selected using the SARG observations obtained during commissioning time and the first nights assigned to this project. We are checking for undetected double line binaries, rotational broadening and activity indicators. After April 2001 run, we have already obtained first epoch spectra for 55 pairs (only one still missing). We identified 2 double lines  and 1 single line spectroscopic binaries and two stars with velocity difference incompatible with the orbital motion of the wide binary. These stars were excluded from the sample. The final sample would be composed by about 100 stars (50 pairs).  A smaller sample will likely lead to a number of detections insufficient  to draw any significant conclusion.

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SARG Commissioning Results

• We are analyzing the iodine cell data using  the code developed at ESO (Endl et al. 2000), that was already tested for ESO-CES planet search and led to the discoveries of the planets around the stars i Hor (Kürster et al. 2000) and e Eri (Hatzes et al 2000). From a partial (only five orders out 22 with iodine lines) and preliminary analysis of the data acquired during the SARG commissioning time, we have already achieved a medium-term (a few months baseline) radial velocity precision of 5 m/s on the constant radial velocity star t Ceti and we have measured velocties for 51 Peg that fit very well the known orbit. The analysis of the full spectral format and the fine tuning of the instrument profile modeling parameters could yield further improvements. Thus SARG will match (and possibly overcome) the best instruments in this field (3 m/s at Keck, Butler et al. 2000).

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• Radial velocities of the planet-harbouring star 51 Peg from SARG Commissioning observations (August-November 2000). The known orbit (Marcy et al. 1997 with the updating from www.exoplanets.org) is overplotted.

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• An important by-product of the radial velocity measurements using the iodine cell technique is the determination of the spectrograph instrument profile. The Figure shows the run of the FWHM and asymmetry of SARG instrument  profile along the order for a few spectral orders (left panel) and the Instrument profiles at the center of order 115 in three different nights (right panel).

   

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• Non-interacting main sequence binaries with different chemical composition: evidences of infall of rocky material?

We performed a careful differential abundance analysis of individual components of six main sequence binaries with separations of a few hundreds of AU. To reduce analysis concerns, we selected systems with almost equal mass components. We were able to derive differential abundances of several elements with errors down to 0.01 dex in the best cases. We found that in four systems the two components have the same chemical composition, within these very severe limits. However, clear differences were found for the two remaining systems (HD 219542 and HD 200466), in both cases the primaries being more Fe-rich than the secondaries, by 0.091 ± 0.009 and 0.053 ±  0.024 dex respectively. Similar differences were found for most of the elements considered in our analysis; however, we found no appreciable difference for volatile elements and a trend for increasing abundance differences with increasing condensation temperature for individual elements, a result similar to that found for some single stars with planets by Smith et al. (2001). Finally, we note that HD219542A has a Li-abundance comparable to those of Li-rich stars in old open clusters, while no Li is detected in the slightly cooler HD219542B. We suggest that the primaries of these two systems have accreted rocky planets or the inner dust-rich part of a protoplanetary disk, likely due to gravitational perturbation caused by the presence of the companion.

Zipped Accepted Article : PDF (249 KB), PS (499 KB), PS ZIP(106 KB)

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