Direct diameter measurement of a star filling its Roche Lobe: The semi-detached binary SS Leporis spatially resolved with VINCI/VLTI

Stellar evolution in close binary systems is strongly influenced by mass transfer from one star to the other when one component fills its zero-velocity surface or Roche Lobe. SS Lep is a fairly nearby close binary showing the Algol paradox and a shell spectrum, both indicative of (past) mass transfer. To study the process of mass transfer and its evolutionary consequences, we aim at a direct characterisation of the spatial dimensions of the different components of SS Lep with IR interferometry. We use VINCI/VLTI interferometric observations in the K band and photometric observations from the UV to the far-IR. The visibilities are interpreted with simple geometrical models and the Spectral Energy Distribution (SED) is decomposed into the three main components: A star, M star and dust shell/disk. From the SED, we find that the main emitters in the K band are the M star and the circumstellar environment. Both are spatially resolved with the VINCI observations, showing the excess to be circumbinary and showing the M star to have a size equal to its Roche Lobe. We conclude that we have, for the first time, directly resolved a star filling its Roche Lobe. The resulting mass transfer is probably the cause of (1) the circumbinary dust disk of which we see the hot inner region spatially resolved in our observations, (2) the unusually high luminosity of the A star and (3) the shell spectrum seen in the UV and optical spectra.Comment: 4 pages, 2 figures, accepted for publication in A&A Letters on 26/05/200

Resolving the disk rotation of HD 97048 and HD 100546 in the [O I] 6300A line: evidence for a giant planet orbiting HD 100546

Aims. We intend to spatially and spectrally resolve the [O I] emission region in two nearby Herbig stars. Methods. We present high-resolution (R = 80,000) VLT/UVES echelle spectra of the [O I] 6300A line in the Herbig Ae/Be stars HD 97048 and HD 100546. Apart from the spectral signature, also the spatial extent of the [O I] emission region is investigated. For both stars, we have obtained spectra with the slit positioned at different position angles on the sky. Results. The [O I] emission region of HD 100546 appears to be coinciding with the dust disk, its major axis located at 150+/-11 degrees east of north. The SE part of the disk moves towards the observer, while the NW side is redshifted. The [O I] emission region rotates counterclockwise around the central star. For HD 97048, the position angle of the emission region is 160+/-19 degrees east of north, which is the first determination of this angle in the literature. The southern parts of the disk are blueshifted, the northern side moves away from us. Our data support the idea that a gap is present at 10AU in the disk of HD 100546. Such a gap is likely planet-induced. We estimate the mass and orbital radius of this hypothetical companion responsible for this gap to be 20 Jupiter masses and 6.5 AU respectively. Conclusions. Based on temporal changes in the [O I] line profile, we conclude that inhomogeneities are present in the [O I] emission region of HD 100546. These ``clumps'' could be in resonance with the suggested companion, orbiting the central star in about 11 yr. If confirmed, these observations could point to the existence of an object straddling the line between giant planet and brown dwarf in a system as young as 10 million years.Comment: 13 pages, 8 figures. Accepted for publication in Astronomy & Astrophysics (28/11/2005

On the interplay between flaring and shadowing in disks around Herbig Ae/Be stars

Based on the SED, Herbig stars have been categorized into two observational groups, reflecting their overall disk structure: group I members have disks with a higher degree of flaring than their group II counterparts. We investigate the 5-35 um Spitzer IRS spectra of a sample of 13 group I sources and 20 group II sources. We focus on the continuum emission to study the underlying disk geometry. We have determined the [30/13.5] and [13.5/7] continuum flux ratios. The 7-um flux excess with respect to the stellar photosphere is measured, as a marker for the strength of the near-IR emission produced by the inner disk. We have compared our data to self-consistent passive-disk model spectra, for which the same quantities were derived. We confirm the literature result that the difference in continuum emission between group I and II sources can largely be explained by a different amount of small dust grains. However, we report a strong correlation between the [30/13.5] and [13.5/7] flux ratios for Meeus group II sources. Moreover, the [30/13.5] flux ratio decreases with increasing 7-um excess for all targets in the sample. To explain these correlations with the models, we need to introduce an artificial scaling factor for the inner disk height. In roughly 50% of the Herbig Ae/Be stars in our sample, the inner disk must be inflated by a factor 2 to 3 beyond what hydrostatic calculations predict. The total disk mass in small dust grains determines the degree of flaring. We conclude, however, that for any given disk mass in small dust grains, the shadowing of the outer (tens of AU) disk is determined by the scale height of the inner disk (1 AU). The inner disk partially obscures the outer disk, reducing the disk surface temperature. Here, for the first time, we prove these effects observationally.Comment: 4 pages, 3 figures, accepted by A&

Evidence for CO depletion in the inner regions of gas-rich protoplanetary disks

We investigate the physical properties and spatial distribution of Carbon Monoxide (CO) gas in the disks around the Herbig Ae/Be stars HD 97048 and HD 100546. Using high-spectral-resolution 4.588-4.715 $\mu$m spectra containing fundamental CO emission taken with CRIRES on the VLT, we probe the circumstellar gas and model the kinematics of the emission lines. By using spectro-astrometry on the spatially resolved targets, we constrain the physical size of the emitting regions in the disks. We resolve, spectrally and spatially, the emission of the $^{13}$CO v(1-0) vibrational band and the $^{12}$CO $v=1-0, v=2-1, v=3-2$ and $v=4-3$ vibrational bands in both targets, as well as the $^{12}$CO $v=5-4$ band in HD 100546. Modeling of the CO emission with a homogeneous disk in Keplerian motion, yields a best fit with an inner and outer radius of the CO emitting region of 11 and $\geq$ 100 AU for HD 97048. HD 100546 is not fit well with our model, but we derive a lower limit on the inner radius of 8 AU. The fact that gaseous [OI] emission was previously detected in both targets at significantly smaller radii suggests that CO may be effectively destroyed at small radii in the surface layers of these disksComment: v2: Letter format has been changed to Paper format; Change in the focus of the paper towards CO depletion; Major changes in text; Change of title. Submitted to A&A, 14/10/2008. Accepted by A&A, 17/04/200

Genotypic characterisation and cluster analysis of Campylobacter jejuni isolates from domestic pets, human clinical cases and retail food

The genetic similarity of Campylobacter jejuni isolates from pets, compared to human clinical cases and retail food isolates collected in Ireland over 2001-2006 was investigated by cluster analysis of pulsed-field gel electrophoresis (PFGE) fingerprinting profiles. Comparison of the PFGE profiles of 60 pet isolates and 109 human isolates revealed that seven (4.1%) profiles were grouped in clusters including at least one human and one pet C. jejuni isolate. In total six (1.6%) of 60 pet and 310 food profiles were in clusters with at least one food and one pet C. jejuni isolate. The detection of only a small number of genetically indistinguishable isolates by PFGE profile cluster analysis from pets and from humans with enteritis in this study suggests that pets are unlikely to be an important reservoir for human campylobacteriosis in Ireland. However, genetically indistinguishable isolates were detected and C. jejuni from pets may circulate and may contribute to clinical infections in humans. In addition, contaminated food fed to pets may be a potential source of Campylobacter infection in pets, which may subsequently pose a risk to humans

A survey for nanodiamond features in the 3 micron spectra of Herbig Ae/Be stars

We have carried out a survey of 60 Herbig Ae/Be stars in the 3 micron wavelength region in search for the rare spectral features at 3.43 and 3.53 micron. These features have been attributed to the presence of large, hot, hydrogen-terminated nanodiamonds. Only two Herbig Ae/Be stars, HD 97048 and Elias 3-1 are known to display both these features. We have obtained medium-resolution spectra (R ~2500) with the ESO near-IR instrument ISAAC in the 3.15-3.65 micron range. In our sample, no new examples of sources with prominent nanodiamond features in their 3 micron spectra were discovered (detection rate less than 4%). We report tentative 3.53 micron detections in V921 Sco (=CD-42.11721), HD 163296 and T CrA. The sources which display the nanodiamond features are not exceptional in the group of Herbig stars with respect to disk properties, stellar characteristics, or disk and stellar activity. Moreover, the nanodiamond sources are very different from each other in terms of these parameters. We do not find evidence for a recent supernova in the vicinity of any of the nanodiamond sources. We have analyzed the PAH 3.3 micron feature and the Pfund delta hydrogen emission line, two other spectral features which occur in the 3 micron wavelength range. We reinforce the conclusion of previous authors that flared-disk systems display significantly more PAH emission than self-shadowed-disk sources. The Pf delta line detection rate is higher in self-shadowed-disk sources than in the flared-disk systems. We discuss the possible origin and paucity of the (nano)diamond features in Herbig stars. Different creation mechanisms have been proposed in the literature, amongst others in-situ and supernova-induced formation. Our data set is inconclusive in proving or disproving either formation mechanism.Comment: 22 pages, 9 figures, 5 tables; accepted for publication in A&A (acceptance date 16/06/2006

Spatially extended PAHs in circumstellar disks around T Tauri and Herbig Ae stars

Our aim is to determine the presence and location of the emission from polycyclic aromatic hydrocarbons (PAHs) towards low and intermediate mass young stars with disks using large aperture telescopes. VLT-VISIR N-band spectra and VLT-ISAAC and VLT-NACO L-band spectra of 29 sources are presented, spectrally resolving the 3.3, 8.6, 11.2, and 12.6 micron PAH features. Spatial-extent profiles of the features and the continuum emission are derived and used to associate the PAH emission with the disks. The results are discussed in the context of recent PAH-emission disk models. The 3.3, 8.6, and 11.2 micron PAH features are detected toward a small fraction of the T Tauri stars, with typical upper limits between 1E-15 and 5E-17 W/m^2. All 11.2 micron detections from a previous Spitzer survey are confirmed with (tentative) 3.3 micron detections, and both the 8.6 and the 11.2 micron features are detected in all PAH sources. For 6 detections, the spatial extent of the PAH features is confined to scales typically smaller than 0.12-0.34'', consistent with the radii of 12-60 AU disks at their distances (typically 150 pc). For 3 additional sources, WL 16, HD 100546, and TY CrA, one or more of the PAH features are more extended than the hot dust continuum of the disk, whereas for Oph IRS 48, the size of the resolved PAH emission is confirmed as smaller than for the large grains. For HD 100546, the 3.3 micron emission is confined to a small radial extent of 12 +- 3 AU, most likely associated with the outer rim of the gap in this disk. Gaps with radii out to 10-30 AU may also affect the observed PAH extent for other sources. For both Herbig Ae and T Tauri stars, the small measured extents of the 8.6 and 11.2 micron features are consistent with larger (>= 100 carbon atoms) PAHs.Comment: 14 pages, 17 figures, accepted for publication in A&

The Structure of Protoplanetary Disks Surrounding Three Young Intermediate Mass Stars. I. Resolving the disk rotation in the [OI] 6300 \AA line

We present high spectral resolution optical spectra of three young intermediate mass stars, in all of which we spectrally resolve the 6300 Angstrom [OI] emission line. Two of these have a double peaked line profile. We fit these data with a simple model of the [OI] emission caused by photo-dissociation of OH molecules in the upper layer of a circumstellar disk by stellar UV radiation and thus translate the Doppler broadened [OI] emission profile into an amount of emission as a function of distance from the central star. The resulting spectra are in agreement with the expected disk shapes as derived from their spectral energy distribution. We find evidence for shadowing by an inner rim in the disk surrounding HD101412 and see a flaring disk structure in HD179218 while the [OI] spectrum of HD135344 is more complex. The [OI] emission starts for all three targets at velocities corresponding to their dust sublimation radius and extends up to radii of 10 -- 90 AU. This shows that this method can be a valuable tool in the future investigation of circumstellar disks.Comment: 11 pages, 19 figures, accepted in A&A on 04/02/2008; added reference

Tourists' perceptions of the free-roaming dog population in Samoa

A study was undertaken to establish how visiting tourists to Samoa perceived free-roaming dogs (Canis familiaris) and their management, additionally some factors that influence their perceptions were assessed. Questionnaires were administered to 281 tourists across Samoa over 5 weeks. Free-roaming dogs were seen by 98.2% (n = 269/274) of respondents, with 64.9% (n = 137/211) reporting that their presence had a negative effect on overall holiday experience. Respondents staying in the Apia (capital city) area were more likely to consider dogs a problem (p < 0.0001), and there was a significant association between whether the respondent owned a dog and if they thought dogs were a nuisance in Samoa (p < 0.003). Forty-four percent (20/89) of non-dog owners agreed that dogs were a nuisance compared to 22% (80/182) of dog owners. The majority felt that dogs required better control and management in Samoa (81%, n = 222) and that there were too many “stray” dogs (67.9%, n = 188). More respondents were negatively affected by the dogs’ presence (64.9%, 137/211), and felt that the dogs made their holiday worse, than respondents that felt the dogs’ presence improved their holiday experience (35.1%, 74/211). Most respondents stated that the dogs had a low impact (one to three; 68%, 187/275) on their stay in Samoa, whilst 24% (65/275) and 8% (23/275) stated they had a medium or high impact, respectively, on their stay. Respondents showed strong support for humane population management. Free-roaming dogs present a complex problem for Samoa and for its tourism industry in particular. The findings of this study further support the need for more discussion and action about the provision of veterinary services and population management for dogs in Samoa. It also provides information complementing an earlier study of the attitudes of local Samoans