57 research outputs found
The TEXES Survey For H-2 Emission From Protoplanetary Disks
No full textWe report the results of a search for pure rotational molecular hydrogen emission from the circumstellar environments of young stellar objects with disks using the Texas Echelon Cross Echelle Spectrograph (TEXES) on the NASA Infrared Telescope Facility and the Gemini North Observatory. We searched for mid-infrared H-2 emission in the S(1), S(2), and S(4) transitions. Keck/NIRSPEC observations of the H-2 S(9) transition were included for some sources as an additional constraint on the gas temperature. We detected H-2 emission from 6 of 29 sources observed: AB Aur, DoAr 21, Elias 29, GSS 30 IRS 1, GV Tau N, and HL Tau. Four of the six targets with detected emission are class I sources that show evidence for surrounding material in an envelope in addition to a circumstellar disk. In these cases, we show that accretion shock heating is a plausible excitation mechanism. The detected emission lines are narrow (similar to 10 km s(-1)), centered at the stellar velocity, and spatially unresolved at scales of 0.4 '', which is consistent with origin from a disk at radii 10-50 AU from the star. In cases where we detect multiple emission lines, we derive temperatures greater than or similar to 500 K from similar to 1 M-circle plus of gas. Our upper limits for the nondetections place upper limits on the amount of H-2 gas with T > 500 K of less than a few Earth masses. Such warm gas temperatures are significantly higher than the equilibrium dust temperatures at these radii, suggesting that the gas is decoupled from the dust in the regions that we are studying and that processes such as UV, X-ray, and accretion heating may be important.NSF AST 06-07312, AST 07-08074NASA NNG04GG92GAstronom
Design for a near-infrared immersion echelle spectrograph: breaking the R=100,000 barrier from 1.5 to 5 μm
No full textHIGH-RESOLUTION SPECTROSCOPY DURING ECLIPSE OF THE YOUNG SUBSTELLAR ECLIPSING BINARY 2MASS 0535–0546. I. PRIMARY SPECTRUM: COOL SPOTS VERSUS OPACITY UNCERTAINTIES
No full textThe Formation of Fullerenes in Planetary Nebulae
No full textIn the last decade, fullerenes have been detected in a variety of astrophysical environments, with the majority being found in planetary nebulae. Laboratory experiments have provided us with insights into the conditions and pathways that can lead to fullerene formation, but it is not clear precisely what led to the formation of astrophysical fullerenes in planetary nebulae. We review some of the available evidence, and propose a mechanism where fullerene formation in planetary nebulae is the result of a two-step process where carbonaceous dust is first formed under unusual conditions; then, the fullerenes form when this dust is being destroyed
High-resolution Br γ spectro-interferometry of the transitional Herbig Ae/Be star HD 100546 : a Keplerian gaseous disc inside the inner rim
No full textACC acknowledges support from CNPq (grant 308985/2009-5). JDI gratefully acknowledges funding from the European Union FP7-2011 under grant agreement no. 284405. RGV acknowledges the support from FAPESP (grant 2012/20364-4).We present spatially and spectrally resolved Br γ emission around the planet-hosting, transitional Herbig Ae/Be star HD 100546. Aiming to gain insight into the physical origin of the line in possible relation to accretion processes, we carried out Br γ spectro-interferometry using AMBER/VLTI from three different baselines achieving spatial and spectral resolutions of 2-4 mas and 12 000. The Br γ visibility is larger than that of the continuum for all baselines. Differential phases reveal a shift between the photocentre of the Br γ line-displaced~0.6mas (0.06 au at 100 pc) NE from the star-and that of the K-band continuum emission-displaced ~0.3 mas NE from the star. The photocentres of the redshifted and blueshifted components of the Br γ line are located NW and SE from the photocentre of the peak line emission, respectively. Moreover, the photocentre of the fastest velocity bins within the spectral line tends to be closer to that of the peak emission than the photocentre of the slowest velocity bins. Our results are consistent with a Br γ-emitting region inside the dust inner rim (≲0.25 au) and extending very close to the central star, with a Keplerian, disc-like structure rotating counter-clockwise, and most probably flared (~25°). Even though the main contribution to the Br γ line does not come from gas magnetically channelled on to the star, accretion on to HD 100546 could be magnetospheric, implying a mass accretion rate of a few 10-7 M⊙ yr-1. This value indicates that the observed gas has to be replenished on time-scales of a few months to years, perhaps by planet-induced flows from the outer to the inner disc as has been reported for similar systems.Peer reviewe
High-resolution Near-infrared Spectroscopy of HD 100546. II. Analysis of Variable Rovibrational CO Emission Lines
No full textWe present observations of rovibrational CO in HD 100546 from four epochs spanning 2003 January through 2010 December. We show that the equivalent widths of the CO lines vary during this time period with the v = 1–0 CO lines brightening more than the UV fluoresced lines from the higher vibrational states.While the spectroastrometric signal of the hot band lines remains constant during this period, the spectroastrometric signal of the v = 1–0 lines varies substantially. At all epochs, the spectroastrometric signals of the UV fluoresced lines are consistent with the signal one would expect from gas in an axisymmetric disk. In 2003, the spectroastrometric signal of the v = 1–0 P26 line was symmetric and consistent with emission from an axisymmetric disk. However, in 2006 there was no spatial offset of the signal detected on the red side of the profile, and in 2010 the spectroastrometric offset was yet more strongly reduced toward zero velocity. A model is presented that can explain the evolution of the equivalent width of the v = 1–0 P26 line and its spectroastrometric signal by adding to the system a compact source of CO emission that orbits the star near the inner edge of the disk. We hypothesize that such emission may arise from a circumplanetary disk orbiting a gas giant planet near the inner edge of the circumstellar disk. We discuss how this idea can be tested observationally and be distinguished from an alternative interpretation of random fluctuations in the disk emission
Search for Search for Close Binaries of Close Binaries of Herbig Herbig Ae Ae/Be Stars /Be Stars
No full textAbstract We present the analysis of high-resolution near-infrared (NIR) adaptive optics images of a sample of 42 Herbig Ae/Be stars (HAEBE) obtained with NIRI/Altair at Gemini North. Companions can be detected as close as 0.1 arcsec and up to 5 magnitudes fainter in the best conditions. In our sample, 9 binaries were found with typical detection limits ρ > 0.087 for small dK and dK < 9.7 for larger ρ. Objects as faint as dK = 5 could be detected at ρ > 0.3. About About Herbig Herbig Ae Ae Be stars Be stars Characteristics of HAEBE Stars -they are pre-main sequence stars with spectral type B through F -they show emission lines and NIR excess associated to a circumstellar disk -they are intermediate-mass stars with masses between 2-8 solar masses Their study will provide a deeper understanding of the formation of HAEBE stars, important for modeling the formation of stars as function of mass and posing additional constrains on star formation models. show a correlation between clustering and spectral type (Testi et al 1997). Observations indicate that HAEBE Stars Summary of the project The project consists in conducting a photometric and spectroscopic survey of HAEBE stars to detect multiple systems and to investigate the nature of the companions. The sample consists of all sources listed i
Multiplicity of Herbig Ae/Be stars
No full textAbstract. One of the most interesting constraints on star formation models comes from the study of multiplicity of young stars as a function of mass. While multiplicity studies of low-mass T Tauri stars have been quite exhaustive, an unbiased and systematic investigation of multiplicity among intermediate-mass Herbig Ae/Be (HAEBE) stars is still lacking. We are therefore conducting a photometric and spectroscopic survey of HAEBE stars to detect companions, establish their physical association with the primary and investigate their properties. The frequency and degree of multiplicity of HAEBE systems will provide new constraints on their formation mechanisms. In this paper we present preliminary results of the high resolution imaging part of the survey, carried out with the adaptive optics system Altair-NIRI on Gemini North. Of 72 stars observed, we find 44 possible binaries or multiples, including at least 25 not previously known
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