6 research outputs found
Ultra-high-resolution observations of Ca+ ions in the local interstellar medium
We present ultra-high-resolution (0.3 km s-1 FWHM) spectra of the interstellar Ca K line towards the nearby starsα Oph, α Gru and α Eri. These are the highest resolution absorption-line spectra yet obtained of clouds located within the local interstellar bubble. They have enabled us to resolve the line profiles fully, and reveal structure within components which have, until now, been considered as arising in single clouds. The velocity dispersions (b-values) of the identified components all have well-determined values in the range 1.4-2.3 km s-1, consistent with thermal broadening at temperatures in the range 5000-13 000 K
Observations of 51 Ophiuchi with MIDI at the VLTI
We present interferometric observations of the Be star 51 Ophiuchi. These
observations were obtained during the science demonstration phase of the MIDI
instrument at the Very Large Telescope Interferometer (VLTI). Using MIDI, a
Michelson 2 beam combiner that operates at the N band (8 to 13 microns), we
obtained for the first time observations of 51 Oph in the mid-infrared at
high-angular resolution. It is currently known that this object presents a
circumstellar dust and gas disk that shows a very different composition from
other Herbig Ae disks. The nature of the 51 Oph system is still a mystery to be
solved. Does it have a companion? Is it a protoplanetary system? We still don't
know. Observations with MIDI at the VLTI allowed us to reach high-angular
resolution (20 mas).We have several uv points that allowed us to constrain the
disk model. We have modeled 51 Oph visibilities and were able to constrain the
size and geometry of the 51 Oph circumstellar disk.Comment: 5 pages, 3 figures, 2 tables, to be published in the proceedings of
"The Power of Optical / IR Interferometry: Recent Scientific Results and 2nd
Generation VLTI Instrumentation", Garching, April 4-8, 200
A study of Vega-like stars and their circumstellar dust
SIGLEAvailable from British Library Document Supply Centre-DSC:DXN024149 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
SCUBA photometry of candidate Vega-like sources
New SCUBA measurements at millimetre wavelengths are presented for a sample of Vega-like stars. Six stars were detected, while sensitive upper limits were obtained for a further 11 sources. Most of the sample selected from a recent catalogue of Vega-like stars have infrared excesses similar to those of the prototype Vega-like stars α Lyr and α PsA. Their IR–submm spectral indices are steep, indicating that the submm emission from the discs is dominated by grains which are smaller than the wavelength of observation and that only small grains exist in those dusty discs. HD 98800 has an IR–submillimetre spectral index of less than two, which suggests that grains have grown to more than 0.3 mm in size. Hipparcos parallax data for HD 42137 and HD 123160 suggest that these two stars are giants rather than dwarfs, similar to the situation previously found for HD 233517. Dust masses, or upper limits, were derived for the sample; these indicate that most of the sources do not have as much dust as Herbig Ae/Be or T Tauri stars, but are likely to have dust masses comparable to those of the prototype Vega-like stars