arXiv subjects

T. Stanke

Publications and source records attributed to T. Stanke.

25 records · Page 2Linked to original sources

arXiv2009

Extremely high velocity gas from the massive YSOs in IRAS 17233-3606

Molecular outflows from high-mass young stellar objects provide an excellent way to study the star formation process, and investigate if they are scaled-up versions of their low-mass counterparts. We selected the nearby massive star forming region IRAS 17233-3606 in order to study the kinematics and physics along the molecular outflow(s) originating from this source. We observed IRAS 17233-3606 in CO, a typical tracer of gas associated with molecular outflow, with the Submillimeter Array in the (2-1) transition, and with the APEX telescope in the higher excitation (6-5) line. Additional infrared H2 observations were performed with the UKIRT telescope. The CO data were analysed using a LVG approach. Our data resolve the previously detected molecular outflow in at least three different components, one of them with a high collimation factor ~4, and characterised by emission at extremely high velocities (|v-v_{LSR}|>120 km s^{-1}). The estimate of the kinematical outflow parameters are typical of massive YSOs, and in agreement with the measured bolometric luminosity of the source. The kinematic ages of the flows are in the range 10^2-10^3 yr, and therefore point to young objects that still did not reach the main sequence.

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arXiv2008

A census of molecular hydrogen outflows and their sources along the Orion A molecular ridge: characteristics and overall distribution

We present wide-field near-IR images of Orion A. K and H2 1-0S(1) images of a contiguous 8 sqr degree region are compared to photometry from Spitzer and dust-continuum maps obtained with MAMBO and SCUBA. We also measure proper motions for H2 features in 33 outflows. We increase the number of known H2 outflows in Orion A to 116. A total of 111 H2 flows were observed with Spitzer; outflow sources are identified for at least 72 of them. The MAMBO 1200 micron maps cover 97 H2 flows; 57 of them are associated with Spitzer sources and dust cores or extended emission. The H2 jets are widely distributed and randomly orientated; the jets do not appear to be orthogonal to large-scale filaments or even to the small-scale cores. Moreover, H2 jet lengths and opening angles are not obviously correlated with indicators of outflow source age - source spectral index or (sub)millimetre core flux. We demonstrate that H2 jet sources are predominantly protostellar with flat or positive spectral indices, rather than disk-excess (or T Tauri) stars. Most protostars in molecular cores drive H2 outflows. However, not all molecular cores are associated with protostars or H2 jets. On statistical grounds, the H2 jet phase may be marginally shorter than the protostellar phase, though must be considerably shorter than the prestellar phase. In terms of their spectral index, H2 jet sources are indistinguishable from protostars. The few true protostars without H2 jets are almost certainly more evolved than their H2-jet-driving counterparts. We also find that protostars that power molecular outflows are no more (nor no less) clustered than protostars that do not. The H2 emission regions in outflows from young stars clearly weaken and fade very quickly, before the source evolves from protostar to pre-main-sequence star.

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arXiv2003

Multiple outflows in IRAS 19410+2336

PdBI high-spatial resolution CO observations combined with near-infrared H2 data disentangle at least 7 (maybe even 9) molecular outflows in the massive star-forming region IRAS19410+2336. Position-velocity diagrams of the outflows reveal Hubble-like relationships similar to outflows driven by low-mass objects. Estimated accretion rates are of the order 10^-4 Msun/yr, sufficiently high to overcome the radiation pressure and form massive stars via disk-mediated accretion processes. The single-dish large-scale mm continuum cores fragment into several compact condensations at the higher spatial resolution of the PdBI which is expected due to the clustering in massive star formation. While single-dish data give a simplified picture of the source, sufficiently high spatial resolution resolves the structures into outflows resembling those of low-mass star-forming cores. We interpret this as further support for the hypothesis that massive stars do form via disk-accretion processes similar to low-mass stars.

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arXiv2003

Molecular outflows in the young open cluster IC348

We present a wide-field survey of the young open cluster IC348 for molecular H2 outflows. Outflow activity is only found at its south-western limit, where a new subcluster of embedded sources is in an early phase of its formation. If the IC348 cluster had been built up by such subclusters forming at different times, this could explain the large age-spread that Herbig (1998) found for the IC348 member stars. In addition to several compact groups of H2 knots, our survey reveals a large north-south oriented outflow, and we identify the newly discovered far-infrared and mm-object IC348MMS as its source. New deep images in the 1-0 S(1) line of molecular hydrogen trace the HH211 jet and counterjet as highly-collimated chains of knots, resembling the interferometric CO and SiO jets. This jet system appears rotated counter-clockwise by about 3 degrees with respect to the prominent H2 bow shocks. Furthermore, we resolve HH211-mm as a double point-like source in the mm-continuum.

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arXiv2002

Hard X-ray emission from a young massive star-forming cluster

We report the detection of hard X-ray emission (>2 keV) from a number of point sources associated with the very young massive star-forming region IRAS 19410+2336. The X-ray emission is detected from several sources located around the central and most deeply embedded mm continuum source, which remains undetected in the X-ray regime. All X-ray sources have K-band counterparts, and those likely belonging to the evolving massive cluster show near-infrared colors in the 2MASS data indicative of pre-main-sequence stages. The X-ray luminosities around 10^{31} erg/s are at the upper end of luminosities known for low-mass pre-main-sequence sources, and mass estimates based on the infrared data indicate that at least some of the X-ray detected sources are intermediate-mass objects. Therefore, we conclude that the X-ray emission is due to intermediate-mass pre-main-sequence Herbig Ae/Be stars or their precursors. The emission process is possibly due to magnetic star-disk interaction as proposed for their low-mass counterparts.

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arXiv2001

The ROSAT Deep Survey: VI. X-ray sources and Optical identifications of the Ultra Deep Survey

We describe in this paper the ROSAT Ultra Deep Survey (UDS), an extension of the ROSAT Deep Survey (RDS) in the Lockman Hole. The UDS reaches a flux level of 1.2 x 10E-15 erg/cm2/s in 0.5-2.0 keV energy band, a level ~4.6 times fainter than the RDS. We present nearly complete spectroscopic identifications (90%) of the sample of 94 X-ray sources based on low-resolution Keck spectra. The majority of the sources (57) are broad emission line AGNs (type I), whereas a further 13 AGNs show only narrow emission lines or broad Balmer emission lines with a large Balmer decrement (type II AGNs) indicating significant optical absorption. The second most abundant class of objects (10) are groups and clusters of galaxies (~11%). Further we found five galactic stars and one ''normal'' emission line galaxy. Eight X-ray sources remain spectroscopically unidentified. The photometric redshift determination indicates in three out of the eight sources the presence of an obscured AGN in the range of 1.2 < z < 2.7. These objects could belong to the long-sought population of type 2 QSOs, which are predicted by the AGN synthesis models of the X-ray background. Finally, we discuss the optical and soft X-ray properties of the type I AGN, type II AGN, and groups and clusters of galaxies, and the implications to the X-ray backround.

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arXiv1999

Keck Spectra of Brown Dwarf Candidates and a Precise Determination of the Lithium Depletion Boundary in the Alpha Persei Open Cluster

We have identified twenty-seven candidate very low mass members of the relatively young Alpha Persei open cluster from a six square degree CCD imaging survey. Based on their I magnitudes and the nominal age and distance to the cluster, these objects should have masses less than 0.1 Msunif they are cluster members. We have subsequently obtained intermediate resolution spectra of seventeen of these objects using the Keck II telescope and LRIS spectrograph. We have also obtained near-IR photometry for many of the stars. Our primary goal was to determine the location of the "lithium depletion boundary" and hence to derive a precise age for the cluster. We detect lithium with equivalent widths greater than or equal to 0.4 Åin five of the program objects. We have constructed a color-magnitude diagram for the faint end of the Alpha Persei main sequence. These data allow us to accurately determine the Alpha Persei single-star lithium depletion boundary at M(I$_C$) = 11.47, M(Bol) = 11.42, (R-I)$_{C0}$ = 2.12, spectral type M6.0. By reference to theoretical evolutionary models, this converts fairly directly into an age for the Alpha Persei cluster of 90 $\pm$ 10 Myr. At this age, the two faintest of our spectroscopically confirmed members should be sub-stellar (i.e., brown dwarfs) according to theoretical models.

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