arXiv subjects

G. van der Plas

Publications and source records attributed to G. van der Plas.

41 records · Page 3Linked to original sources

arXiv2010

An Inner Gaseous Disk around the Herbig Be Star MWC 147

We present high-spectral-resolution, optical spectra of the Herbig Be star MWC 147, in which we spectrally resolve several emission lines, including the [O I] lines at 6300 and 6363°. Their highly symmetric, double-peaked line profiles indicate that the emission originates in a rotating circumstellar disk. We deconvolve the Doppler-broadened [O I] emission lines to obtain a measure of emission as a function of distance from the central star. The resulting radial surface brightness profiles are in agreement with a disk structure consisting of a flat, inner, gaseous disk and a flared, outer, dust disk. The transition between these components at 2 to 3 AU corresponds to the estimated dust sublimation radius. The width of the double-peaked Mg II line at 4481°suggests that the inner disk extends to at least 0.10 AU, close to the corotation radius.

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arXiv2009

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 $μ$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 disks

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arXiv2008

The structure of the protoplanetary disk surrounding three young intermediate mass stars. II. Spatially resolved dust and gas distribution

[Abridged] We present the first direct comparison of the distribution of the gas, as traced by the [OI] 6300 AA emission, and the dust, as traced by the 10 micron emission, in the protoplanetary disk around three intermediate-mass stars: HD 101412, HD 135344 B and HD 179218. N-band visibilities were obtained with VLTI/MIDI. Simple geometrical models are used to compare the dust emission to high-resolution optical spectra in the 6300 AA [OI] line of the same targets. The disks around HD 101412 and HD 135344 B appear strongly flared in the gas, but self-shadowed in the dust beyond ~ 2 AU. In both systems, the 10 micron emission is rather compact (< 2 AU) while the [OI] brightness profile shows a double peaked structure. The inner peak is strongest and is consistent with the location of the dust, the outer peak is fainter and is located at 5-10 AU. Spatially extended PAH emission is found in both disks. The disk around HD 179218 is flared in the dust. The 10 micron emission emerges from a double ring-like structure with the first ring peaking at ~ 1 AU and the second at ~ 20 AU. No dust emission is detected between ~ 3 -- 15 AU. The oxygen emission seems also to come from a flared structure, however, the bulk of this emission is produced between ~ 1 -- 10 AU. This could indicate a lack of gas in the outer disk or could be due to chemical effects which reduce the abundance of OH -- the parent molecule of the observed [OI] emission -- further away from the star. The three systems, HD 179218, HD 135344 B and HD 101412, may form an evolutionary sequence: the disk initially flared becomes flat under the combined action of gas-dust decoupling, grain growth and dust settling.

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arXiv2008

Probing the Early Evolution of Young High-Mass Stars

Near-infrared imaging surveys of high-mass star-forming regions reveal an amazingly complex interplay between star formation and the environment (Churchwell et al. 2006; Alvarez et al. 2004). By means of near-IR spectroscopy the embedded massive young stars can be characterized and placed in the context of their birth site. However, so far spectroscopic surveys have been hopelessly incomplete, hampering any systematic study of these very young massive stars. New integral field instrumentation available at ESO has opened the possibility to take a huge step forward by obtaining a full spectral inventory of the youngest massive stellar populations in star-forming regions currently accessible. Simultaneously, the analysis of the extended emission allows the characterization of the environmental conditions. The Formation and Early Evolution of Massive Stars (FEMS) collaboration aims at setting up a large observing campaign to obtain a full census of the stellar content, ionized material, outflows and PDR's over a sample of regions that covers a large parameter space. Complementary radio, mm and infrared observations will be used for the characterization of the deeply embedded population. For the first eight regions we have obtained 40 hours of SINFONI observations. In this contribution, we present the first results on three regions that illustrate the potential of this strategy.

astro-ph↗

arXiv2008

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

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.

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