arXiv subjects

Nienke van der Marel

Publications and source records attributed to Nienke van der Marel.

95 records · Page 6Linked to original sources

arXiv2013

Gas structure inside dust cavities of transition disks: Oph IRS 48 observed by ALMA

(Abridged) Transition disks are recognized by the absence of emission of small dust grains inside a radius of up to several 10s of AUs. Due to the lack of angular resolution and sensitivity, the gas content of such dust holes has not yet been determined, but is of importance to constrain the mechanism leading to the dust holes. Transition disks are thought to currently undergo the process of dispersal, setting an end to the giant planet formation process. We present new high-resolution observations with the Atacama Large Millimeter/ submillimeter Array (ALMA) of gas lines towards the transition disk Oph IRS 48 previously shown to host a large dust trap. ALMA has detected the $J=6-5$ line of $^{12}$CO and C$^{17}$O around 690 GHz (434 $μ$m) at a resolution of $\sim$0.25$''$ corresponding to $\sim$30 AU (FWHM). The observed gas lines are used to set constraints on the gas surface density profile. New models of the physical-chemical structure of gas and dust in Oph IRS 48 are developed to reproduce the CO line emission together with the spectral energy distribution (SED) and the VLT-VISIR 18.7 $μ$m dust continuum images. Integrated intensity cuts and the total spectrum from models having different trial gas surface density profiles are compared to observations. Using the derived surface density profiles, predictions for other CO isotopologues are made, which can be tested by future ALMA observations of the object. The derived gas surface density profile points to the clearing of the cavity by one or more massive planet/companion rather than just photoevaporation or grain-growth.

astro-ph.SR↗

arXiv2013

A Major Asymmetric Dust Trap in a Transition Disk

The statistics of discovered exoplanets suggest that planets form efficiently. However, there are fundamental unsolved problems, such as excessive inward drift of particles in protoplanetary disks during planet formation. Recent theories invoke dust traps to overcome this problem. We report the detection of a dust trap in the disk around the star Oph IRS 48 using observations from the Atacama Large Millimeter/submillimeter Array (ALMA). The 0.44-millimeter-wavelength continuum map shows high-contrast crescent-shaped emission on one side of the star originating from millimeter-sized grains, whereas both the mid-infrared image (micrometer-sized dust) and the gas traced by the carbon monoxide 6-5 rotational line suggest rings centered on the star. The difference in distribution of big grains versus small grains/gas can be modeled with a vortex-shaped dust trap triggered by a companion.

astro-ph.EP↗

arXiv2013

Outflow forces of low mass embedded objects in Ophiuchus: a quantitative comparison of analysis methods

The outflow force of molecular bipolar outflows is a key parameter in theories of young stellar feedback on their surroundings. The focus of many outflow studies is the correlation between the outflow force, bolometric luminosity and envelope mass. However, it is difficult to combine the results of different studies in large evolutionary plots over many orders of magnitude due to the range of data quality, analysis methods and corrections for observational effects such as opacity and inclination. We aim to determine the outflow force for a sample of low luminosity embedded sources. We will quantify the influence of the analysis method and the assumptions entering the calculation of the outflow force. We use the James Clerk Maxwell Telescope to map 12CO J=3-2 over 2'x2' regions around 16 Class I sources of a well-defined sample in Ophiuchus at 15" resolution. The outflow force is then calculated using seven different methods differing e.g. in the use of intensity-weighted emission and correction factors for inclination. The results from the analysis methods differ from each other by up to a factor of 6, whereas observational properties and choices in the analysis procedure affect the outflow force by up to a factor of 4. For the sample of Class I objects, bipolar outflows are detected around 13 sources including 5 new detections, where the three non-detections are confused by nearby outflows from other sources. When combining outflow forces from different studies, a scatter by up to a factor of 5 can be expected. Although the true outflow force remains unknown, the separation method (separate calculation of dynamical time and momentum) is least affected by the uncertain observational parameters. The correlations between outflow force, bolometric luminosity and envelope mass are further confirmed down to low luminosity sources.

astro-ph.SR↗

arXiv2012

APEX-CHAMP+ high-J CO observations of low-mass young stellar objects: III. NGC 1333 IRAS 4A/4B envelope, outflow and UV heating

NGC 1333 IRAS 4A and IRAS 4B sources are among the best studied Stage 0 low-mass protostars which are driving prominent bipolar outflows. Most studies have so far concentrated on the colder parts (T<30K) of these regions. The aim is to characterize the warmer parts of the protostellar envelope in order to quantify the feedback of the protostars on their surroundings in terms of shocks, UV heating, photodissociation and outflow dispersal. Fully sampled large scale maps of the region were obtained; APEX-CHAMP+ was used for 12CO 6-5, 13CO 6-5 and [CI] 2-1, and JCMT-HARP-B for 12CO 3-2 emissions. Complementary Herschel-HIFI and ground-based lines of CO and its isotopologs, from 1-0 upto 10-9 (Eu/k 300K), are collected at the source positions. Radiative-transfer models of the dust and lines are used to determine temperatures and masses of the outflowing and UV-heated gas and infer the CO abundance structure. Broad CO emission line profiles trace entrained shocked gas along the outflow walls, with typical temperatures of ~100K. At other positions surrounding the outflow and the protostar, the 6-5 line profiles are narrow indicating UV excitation. The narrow 13CO 6-5 data directly reveal the UV heated gas distribution for the first time. The amount of UV-heated and outflowing gas are found to be comparable from the 12CO and 13CO 6-5 maps, implying that UV photons can affect the gas as much as the outflows. Weak [CI] emission throughout the region indicates a lack of CO dissociating photons. Modeling of the C18O lines indicates the necessity of a "drop" abundance profile throughout the envelope where the CO freezes out and is reloaded back into the gas phase, thus providing quantitative evidence for the CO ice evaporation zone around the protostars. The inner abundances are less than the canonical value of CO/H_2=2.7x10^-4, indicating some processing of CO into other species on the grains.

astro-ph.SR↗

arXiv2011

Complex molecules toward low-mass protostars: the Serpens core

Gas-phase complex organic molecules are commonly detected toward high-mass protostellar hot cores. Detections toward low-mass protostars and outflows are comparatively rare, and a larger sample is key to investigate how the chemistry responds to its environment. Guided by the prediction that complex organic molecules form in CH3OH-rich ices and thermally or non-thermally evaporate with CH3OH, we have identified three sight-lines in the Serpens core - SMM1, SMM4 and SMM4-W - which are likely to be rich in complex organics. Using the IRAM 30m telescope, narrow lines (FWHM of 1-2 km s-1) of CH3CHO and CH3OCH3 are detected toward all sources, HCOOCH3 toward SMM1 and SMM4-W, and C2H5OH not at all. Beam-averaged abundances of individual complex organics range between 0.6 and 10% with respect to CH3OH when the CH3OH rotational temperature is applied. The summed complex organic abundances also vary by an order of magnitude, with the richest chemistry toward the most luminous protostar SMM1. The range of abundances compare well with other beam-averaged observations of low-mass sources. Complex organic abundances are of the same order of magnitude toward low-mass protostars and high-mass hot cores, but HCOOCH3 is relatively more important toward low-mass protostars. This is consistent with a sequential ice photochemistry, dominated by CHO-containing products at low temperatures and early times.

astro-ph.GA↗