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The young star beta Pictoris is well known for its dusty debris disk, produced through the grinding down by collisions of planetesimals, kilometre-sized bodies in orbit around the star. In addition to dust, small amounts of gas are also known to orbit the star, likely the result from vaporisation of violently colliding dust grains. The disk is seen edge on and from previous absorption spectroscopy we know that the gas is very rich in carbon relative to other elements. The oxygen content has been more difficult to assess, however, with early estimates finding very little oxygen in the gas at a C/O ratio 20x higher than the cosmic value. A C/O ratio that high is difficult to explain and would have far-reaching consequences for planet formation. Here we report on observations by the far-infrared space telescope Herschel, using PACS, of emission lines from ionised carbon and neutral oxygen. The detected emission from C+ is consistent with that previously reported being observed by the HIFI instrument on Herschel, while the emission from O is hard to explain without assuming a higher-density region in the disk, perhaps in the shape of a clump or a dense torus, required to sufficiently excite the O atoms. A possible scenario is that the C/O gas is produced by the same process responsible for the CO clump recently observed by ALMA in the disk, and that the re-distribution of the gas takes longer than previously assumed. A more detailed estimate of the C/O ratio and the mass of O will have to await better constraints on the C/O gas spatial distribution., Accepted by A&A; 6 pages including 3 figures

A multisite photometric campaign for the Beta Cephei and eclipsing variable 16 Lacertae is reported. 749 h of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry were obtained with ten telescopes during 185 nights. After removing the pulsation contribution, an attempt was made to solve the resulting eclipse light curve by means of the computer program EBOP. Although a unique solution was not obtained, the range of solutions could be constrained by comparing computed positions of the secondary component in the Hertzsprung-Russell diagram with evolutionary tracks. For three high-amplitude pulsation modes, the uvy and the Geneva UBG amplitude ratios are derived and compared with the theoretical ones for spherical-harmonic degrees l, 18 pages, 19 figures, accepted for publication in MNRAS

We report on a recent event in which, after more than a decade of slowly fading, the visual brightness of the massive young binary Z CMa suddenly started to rise by about 1 magnitude in December 1999, followed by a rapid decline to its previous brightness over the next six months. This behaviour is similar to that exhibited by this system around its eruption in February 1987. A comparison of the intrinsic luminosities of the system with recent evolutionary calculations shows that Z CMa may consist of a 16 M_sun B0 IIIe primary star and a ~ 3 M_sun FUOr secondary with a common age of ~ 3 x 10^5 yr. We also compare new high-resolution spectra obtained in Jan. and Feb. 2000, during the recent rise in brightness, with archive data from 1991 and 1996. The spectra are rich in emission lines, which originate from the envelope of the early B-type primary star. The strength of these emission lines increased strongly with the brightness of Z CMa. We interpret the collected spectral data in terms of an accretion disc with atmosphere around the Herbig B0e component of Z CMa, which has expanded during the outbursts of 1987 and 2000. A high resolution profile of the 6300 A [O I] emission line, obtained by us in March 2002 shows an increase in flux and a prominent blue shoulder to the feature extending to ~ -700 km/s, which was much fainter in the pre-outburst spectra. We propose that this change in profile is a result of a strong change in the collimation of a jet, as a result of the outburst at the start of this century., 22 pages, 12 figures, accepted for publication in MNRAS

Red giants are evolved stars which exhibit solar-like oscillations. Although a multitude of stars have been observed with space telescopes, only a handful of red-giant stars were targets of spectroscopic asteroseismic observing projects. We search for solar-like oscillations in the two bright red-giant stars $��$ Psc and $��^1$ Tau from time series of ground-based spectroscopy and determine the frequency of the excess of oscillation power $��_{max}$ and the mean large frequency separation $����$ for both stars. The radial velocities of $��$ Psc and $��^1$ Tau were monitored for 120 and 190 days, respectively. Nearly 9000 spectra were obtained. To reach the accurate radial velocities, we used simultaneous thorium-argon and iodine-cell calibration of our optical spectra. In addition to the spectroscopy, we acquired VLTI observations of $��$ Psc for an independent estimate of the radius. Also 22 days of observations of $��^1$ Tau with the MOST-satellite were analysed. The frequency analysis of the radial velocity data of $��$ Psc revealed an excess of oscillation power around 32 $��$Hz and a large frequency separation of 4.1$\pm$0.1$��$Hz. $��^1$ Tau exhibits oscillation power around 90 $��$Hz, with a large frequency separation of 6.9$\pm$0.2$��$Hz. Scaling relations indicate that $��$ Psc is a star of about $\sim$1 M$_\odot$ and $\sim$10 R$_\odot$. $��^1$ Tau appears to be a massive star of about $\sim$2.7 M$_\odot$ and $\sim$11 R$_\odot$. The radial velocities of both stars were found to be modulated on time scales much longer than the oscillation periods. While the mass of $��^1$ Tau is in agreement with results from dynamical parallaxes, we find a lower mass for $��$ Psc than what is given in the literature. The long periodic variability agrees with the expected time scales of rotational modulation., 15 pages, 15 figures; accepted for publication in A&A

Herschel images in six photometric bands show the thermal emission of the debris disk surrounding beta Pic. In the three PACS bands at 70 micron, 100 micron and 160 micron and in the 250 micron SPIRE band, the disk is well-resolved, and additional photometry is available in the SPIRE bands at 350 micron and 500 micron, where the disk is only marginally resolved. The SPIRE maps reveal a blob to the southwest of beta Pic, coinciding with submillimetre detection of excess emission in the disk. We investigated the nature of this blob. Our comparison of the colours, spectral energy distribution and size of the blob, the disk and the background sources shows that the blob is most likely a background source with a redshift between z =1.0 and z = 1.6.

We present the methodology and some preliminary results of our study of the relationship between a Mira's pulsating photosphere and its surrounding molecular layer(s) throughout several pulsation cycles, based on spatially resolved data. Our dataset consists of archival narrow-band observations in the near-infrared H and K bands obtained with the Palomar Testbed Interferometer between 1999 and 2006, extended with a few nights of VLTI AMBER low spectral resolution data and near-infrared SAAO photometry. The fitted model is the geometric star + layer model proposed by Perrin et al. (2004), in which the physical parameters (diameter and temperature of star and layer; wavelength dependent optical depth of the layer) are given a sinusoidal time dependence., Comment: 2 pages, to be published in ASP Conference Proceedings of the Vienna conference "Why Galaxies Care About AGB Stars II"

We obtained Herschel PACS and SPIRE images of the thermal emission of the debris disk around the A5V star �� Pic. The disk is well resolved in the PACS filters at 70, 100, and 160 ��m. The surface brightness profiles between 70 and 160 ��m show no significant asymmetries along the disk, and are compatible with 90% of the emission between 70 and 160 ��m originating in a region closer than 200 AU to the star. Although only marginally resolving the debris disk, the maps obtained in the SPIRE 250 - 500 ��m filters provide full-disk photometry, completing the SED over a few octaves in wavelength that had been previously inaccessible. The small far-infrared spectral index (�� = 0.34) indicates that the grain size distribution in the inner disk (, Accepted for publication in Astronomy&Astrophysics, Herschel First Results special issue

Gamma Doradus stars are excellent targets for asteroseismology since the gravity modes present in these stars probe the deep stellar interiors. Mode identification will improve the knowledge of these stars considerably. A selected group of Gamma Doradus stars and some candidates were observed with the Mercator telescope to find and/or confirm the periodicities in the light variations and to derive reliable amplitude ratios in different pass bands. A frequency analysis was performed on all new data obtained in the Geneva photometric system. In order to have more reliable and accurate frequencies, the new data were combined with similar data from the literature and with Hipparcos observations. A set of frequencies that minimized the the residuals in a harmonic fit was searched for while allowing means and amplitudes to vary from one observation set to another. Frequencies and amplitudes in the photometric passbands of the Geneva system are given for 21 Gamma Doradus stars. We report the discovery of HD 74504 as a newly found Gamma Doradus star. Our study provides the first extensive multicolour database for the understanding of gravity modes in F-type stars., Electronic tables (5 to 25) not included in this version

International audience; Aims. We study the geometry and kinematics of the circumstellar environment of the Be star Kappa CMa in the Br gamma emission line and its nearby continuum. Methods. We use the VLTI/AMBER instrument operating in the K band which provides a spatial resolution of about 6 mas with a spectral resolution of 1500 to study the kinematics within the disk and to infer its rotation law. In order to obtain more kinematical constraints we also use an high spectral resolution Pa beta line profile obtain in December 2005 at the Observatorio do Pico do Dios, Brazil and we compile V/R line profile variations and spectral energy distribution data points from the literature. Results. Using differential visibilities and differential phases across the Br gamma line we detect an asymmetry in the disk. Moreover, we found that kappa CMa seems difficult to fit within the classical scenario for Be stars, illustrated recently by alpha Arae observations, i.e. a fast rotating B star close to its breakup velocity surrounded by a Keplerian circumstellar disk with an enhanced polar wind. Finally we discuss the possibility for kappa CMa to be a critical rotator with a Keplerian rotating disk and try to see if the detected asymmetry can be interpreted within the "one-armed" viscous disk framework.

The young stellar object MWC 297 has been observed with the VLT interferometer equipped with the AMBER instrument. MWC 297 has been spatially resolved in the continuum with a visibility of 0.50 as well as in the Br gamma emission line where the visibility decrease to a lower value of 0.33. This change in the visibility with the wavelength can be interpreted by the presence of an optically thick disk responsible for the visibility in the continuum and of a stellar wind traced by Br gamma and whose apparent size is 40% larger. We validate this interpretation by building a model of the stellar environment that combines a geometrically thin, optically thick accretion disk model consisting of gas and dust, and a latitude-dependent stellar wind outflowing above the disk surface. The continuum emission and visibilities obtained from this model are fully consistent with the interferometric AMBER data. They agree also with existing optical, near-infrared spectra and other broad-band near-infrared interferometric visibilities. A picture emerges in which MWC 297 is surrounded by an equatorial flat disk that is possibly still accreting and an outflowing wind which has a much higher velocity in the polar region than at the equator. [abridged], Comment: 13 pages; to be published in A&A; Acceptance day: 11/10/2005

We have investigated the infrared spectra of all 46 Herbig Ae/Be stars for which spectroscopic data is available in the ISO data archive. Our quantitative analysis of these spectra focusses on the emission bands linked to polycyclic aromatic hydrocarbons (PAHs), the amorphous 10 micron silicate band and the crystalline silicate band at 11.3 micron. We have detected PAH emission in 57% of the Herbig stars in our sample. Clear examples of differences in the PAH spectra are present within our sample, indicating differences in PAH size, chemistry and/or ionization. Amorphous silicate emission was detected in the spectra of 52% of the sample stars, amorphous silicate absorption in 13%. We have detected crystalline silicate emission in 11 stars (24% of our sample), of which four (9%) also display strong PAH emission. We have classified the sample sources according to the strength of their mid-IR energy distribution. The systems with stronger mid-infared (20-100 um) excesses relative to their near-infrared (1-5 um) excess display significantly more PAH emission than those with weaker mid-infrared excesses. This provides strong observational support for the disk models by Dullemond (2002), in which systems with a flaring disk geometry display a strong mid-infrared excess, whereas those with disks that are strongly shadowed by the puffed-up inner rim of the disk only display modest amounts of mid-infrared emission. The PAH emission is expected to be produced mainly in the part of the disk atmosphere that is directly exposed to radiation from the central star. In this model, self-shadowed disks should display weaker PAH emission than flared disks, consistent with our observations., 27 pages, 26 figures, A&A accepted (22/06/2004)

We present high spectral-resolution optical spectra of 49 Herbig Ae/Be stars in a search for the [O I] 6300.2 A line. The vast majority of the stars in our sample show narrow (FWHM < 100 km/s) emission lines, centered on the stellar radial velocity. Some stars in our sample show double-peaked lines profiles, with peak-to-peak separations of about 10 km/s. The presence and strength of the [O I] line emission appears to be well correlated with the far-infrared energy distribution of each source: stars with a strong excess at 60 micron have in general stronger [O I] emission than stars with weaker 60 micron excesses. We interpret the observed [O I] 6300.2 A line profiles as arising in the surface layers of the protoplanetary disks surrounding Herbig Ae/Be stars., 6 pages, 7 figures; to appear in on-line proceedings Second TPF/Darwin International Conference