arXiv subjects

Peter Zeidler

Publications and source records attributed to Peter Zeidler.

41 records · Page 3Linked to original sources

arXiv2017

A High-Resolution Multiband Survey of Westerlund 2 With the Hubble Space Telescope. III. The present-day stellar mass function

We present a detailed analysis of the spatial distribution of the stellar population and the present-day mass function (PDMF) of the Westerlund 2 (Wd2) region using the data from our high resolution multi-band survey with the Hubble Space Telescope. We used state-of-the-art artificial star tests to determine spatially resolved completeness maps for each of the broad-band filters. We reach a level of completeness of 50 % down to F555W=24.8 mag (0.7 $M_\odot$) and F814W=23.3 mag (0.2 $M_\odot$) in the optical and F125W=20.2 mag and F160W=19.4 mag (both 0.12 $M_\odot$) in the infrared throughout the field of view. We had previously reported that the core of Wd2 consists of two clumps: namely the main cluster (MC) and the northern clump (NC). From the spatial distribution of the completeness corrected population, we find that their stellar surface densities are 1114 stars pc$^{-2}$ and 555 stars pc$^{-2}$, respectively, down to F814W=21.8 mag. We find that the present-day mass function (PDMF) of Wd2 has a slope of $Γ=-1.46 \pm 0.06$, which translates to a total stellar cluster mass of $(3.6 \pm 0.3) \cdot 10^4 M_\odot$. The spatial analysis of the PDMF reveals that the cluster population is mass-segregated, most likely primordial. In addition, we report the detection of a stellar population of spatially uniformly distributed low-mass (<0.15 $M_\odot$) stars, extending into the gas ridges of the surrounding gas and dust cloud, as well as a confined region of reddened stars, likely caused by a foreground CO cloud. We find hints that a cloud-cloud collision might be the origin of the formation of Wd2.

astro-ph.GA↗

arXiv2016

A High-Resolution Multiband Survey of Westerlund 2 With the Hubble Space Telescope. II. Mass accretion in the Pre-Main Sequence Population

We present a detailed analysis of the pre-main-sequence (PMS) population of the young star cluster Westerlund~2 (Wd2), the central ionizing cluster of the HII region RCW 49, using data from a high resolution multi-band survey with the Hubble Space Telescope. The data were acquired with the Advanced Camera for Surveys in the F555W, F814W, and F658N filters and with the Wide Field Camera 3 in the F125W, F160W, and F128N filters. We find a mean age of the region of 1.04+-0.72 Myr. The combination of dereddened F555W and F814W photometry in combination with F658N photometry allows us to study and identify stars with H_alpha excess emission. With a careful selection of 240 bona-fide PMS H_alpha excess emitters we were able to determine their H_alpha luminosity, which has a mean value L(H_alpha)=1.67 x 10^{-31} erg s^{-1}. Using the PARSEC 1.2S isochrones to obtain the stellar parameters of the PMS stars we determined a mean mass accretion rate \dot M_acc=4.43 x 10^{-8} M_sun yr^{-1} per star. A careful analysis of the spatial dependence of the mass-accretion rate suggests that this rate is ~25% lower in center of the two density peaks of Wd2 in close proximity to the luminous OB stars, compared to the Wd2 average. This rate is higher with increasing distance from the OB stars, indicating that the PMS accretion disks are being rapidly destroyed by the far-ultra-violet radiation emitted by the OB population.

astro-ph.SR↗

arXiv2016

Hubble Tarantula Treasury Project. IV. The extinction law

We report on the study of interstellar extinction across the Tarantula nebula (30 Doradus), in the Large Magellanic Cloud, using observations from the Hubble Tarantula Treasury Project in the 0.3 - 1.6 micron range. The considerable and patchy extinction inside the nebula causes about 3500 red clump stars to be scattered along the reddening vector in the colour-magnitude diagrams, thereby allowing an accurate determination of the reddening slope in all bands. The measured slope of the reddening vector is remarkably steeper in all bands than in the the Galactic diffuse interstellar medium. At optical wavelengths, the larger ratio of total-to-selective extinction, namely Rv = 4.5 +/- 0.2, implies the presence of a grey component in the extinction law, due to a larger fraction of large grains. The extra large grains are most likely ices from supernova ejecta and will significantly alter the extinction properties of the region until they sublimate in 50 - 100 Myr. We discuss the implications of this extinction law for the Tarantula nebula and in general for regions of massive star formation in galaxies. Our results suggest that fluxes of strongly star forming regions are likely to be underestimated by a factor of about 2 in the optical.

astro-ph.SR↗

arXiv2015

The VISTA Carina Nebula Survey II. Spatial distribution of the infrared-excess-selected young stellar population

We performed a deep wide-field (6.76 deg^2) near-infrared survey with the VISTA telescope that covers the entire extent of the Carina nebula complex (CNC). The point-source catalog created from these data contains around four million individual objects down to masses of 0.1 M_sun. We present a statistical study of the large-scale spatial distribution and an investigation of the clustering properties of infrared-excesses objects, which are used to trace disk-bearing young stellar objects (YSOs). We find that a (J - H) versus (Ks - [4.5]) color-color diagram is well suited to tracing the population of YSO-candidates (cYSOs) by their infrared excess. We identify 8781 sources with strong infrared excess, which we consider as cYSOs. This sample is used to investigate the spatial distribution of the cYSOs with a nearest-neighbor analysis. The surface density distribution of cYSOs agrees well with the shape of the clouds as seen in our Herschel far-infrared survey. The strong decline in the surface density of excess sources outside the area of the clouds supports the hypothesis that our excess-selected sample consists predominantly of cYSOs with a low level of background contamination. This analysis allows us to identify 14 groups of cYSOs outside the central area. Our results suggest that the total population of cYSOs in the CNC comprises about 164000 objects, with a substantial fraction (~35%) located in the northern, still not well studied parts. Our cluster analysis suggests that roughly half of the cYSOs constitute a non-clustered, dispersed population.

astro-ph.SR↗

arXiv2015

A High-Resolution Multiband Survey of Westerlund 2 With the Hubble Space Telescope I: Is the Massive Star Cluster Double?

We present first results from a high resolution multi-band survey of the Westerlund 2 region with the Hubble Space Telescope. Specifically, we imaged Westerlund 2 with the Advanced Camera for Surveys through the $F555W$, $F814W$, and $F658N$ filters and with the Wide Field Camera 3 in the $F125W$, $F160W$, and $F128N$ filters. We derive the first high resolution pixel-to-pixel map of the color excess $E(B-V)_g$ of the gas associated with the cluster, combining the H$α$ ($F658N$) and Pa$β$ ($F128N$) line observations. We demonstrate that, as expected, the region is affected by significant differential reddening with a median of $E(B-V)_g=1.87$~mag. After separating the populations of cluster members and foreground contaminants using a $(F814W-F160W)$ vs. $F814W$ color-magnitude diagram, we identify a pronounced pre-main-sequence population in Westerlund 2 showing a distinct turn-on. After dereddening each star of Westerlund 2 individually in the color-magnitude diagram we find via over-plotting PARSEC isochrones that the distance is in good agreement with the literature value of $\sim4.16 \pm 0.33$~kpc. With zero-age-main-sequence fitting to two-color-diagrams, we derive a value of total to selective extinction of $R_V=3.95 \pm 0.135$. A spatial density map of the stellar content reveals that the cluster might be composed of two clumps. We estimate the same age of 0.5-2.0 Myr for both clumps. While the two clumps appear to be coeval, the northern clump shows a $\sim 20 \%$ lower stellar surface density.

astro-ph.SR↗