We present high-precision relative radial velocities of the very low mass star VB 10 that were obtained over a time span of 0.61 years as part of an ongoing search for planets around stars at the end ...of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the Very Large Telescope with an ammonia gas cell. The typical internal precision of the measurements is 10 m s{sup -1}. These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo and Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the {approx}1 km s{sup -1} radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M {sub p} > 3 M {sub Jup} and the orbital period and inclination suggested by Pravdo and Shaklan at better than 5{sigma} confidence. We conclude that the planet detection claimed by Pravdo and Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low mass stars.
Near-IR spectroscopy of OB stars with VLT/CRIRES Maria-Fernanda Nieva; Norbert Przybilla; Andreas Seifahrt ...
Bulletin de la Société royale des sciences de Liège,
01/2011, Letnik:
80
Journal Article
Recenzirano
Odprti dostop
We have conducted a pilot observational programme in order to obtain very high resolution near-IR spectra (R~100 000) with wide wavelength coverage in the JHKL bands of early B-type stars with CRIRES ...on the VLT. The sample comprises a B0.2V, a B0 III and a B1.5 III star, which have already been thoroughly analysed by us in previous work in the optical. The stars span a range of about 9000K in effective temperature, thus covering different ions of several elements. A novel data reduction technique was carried out which facilitated telluric lines removal by precise modelling of the Earth’s atmospheric spectrum. We investigate to what extent it is possible to derive atmospheric parameters and chemical abundances of early B-type stars from near- IR spectroscopy only. For this purpose we have extended our non-LTE spectral modelling to applications in the near-IR, based on our state-of-the-art model atoms that were thoroughly tested previously in the optical. Most H, He, C, N, O, Mg and Si lines in the near-IR (some of them resolved for the first time) could be reproduced, allowing atmospheric parameters and chemical abundances to be derived. Some remaining discrepancies between synthetic and observed strong lines, and some lines unidentified due to a lack of atomic data need to be investigated further. We have succesfully tested our modelling techniques and quantitative spectral analysis in the near-IR at high resolution and obtained excellent agreement with previous precision work in the optical. This will allow us to perform reliable spectral analyses of early B-type stars that suffer from strong optical extinction in the future, based on near-IR observations alone.
PDF
