A young double stellar cluster in a HII region, emerging from its parent molecular cloud

We report the properties of a new young double stellar cluster in the region towards IRAS 07141-0920 contained in the HII region Sh2-294. High-resolution optical UBVRI and Halpha images, near-infrared JHKs and H2 filter images were used to make photometric and morphological studies of the point sources and the nebula seen towards Sh2-294. The optical images reveal an emission nebula with very rich morphological details, composed mainly of UV scattered light and of Halpha emission. Contrasting with the bright parts of the nebula, opaque, elongated patches are seen. Our optical photometry confirms that the illuminator of the nebula is likely to be a B0.5V star located at a distance of about 3.2 kpc. Our near-IR images reveal an embedded cluster, extending for about 2 pc and exhibiting sub-clustering: a denser, more condensed, sub-cluster surrounding the optical high-mass B0.5V illuminator star; and a more embedded, optically invisible, sub-cluster located towards the eastern, dark part of the nebula and including the luminous MSX source G224.1880+01.2407, a massive protostellar candidate that could be the origin of jets and extended features seen at 2.12 micron. The double cluster appears to be clearing the remaining molecular material of the parent cloud, creating patches of lower extinction and allowing some of the least reddened members to be detected in the optical images. We find 12 MS and 143 PMS members using 3 different methods: comparison with isochrones in optical colour-magnitude diagrams, detection of near-IR excess, and presence of Halpha emission. The most massive star fits a 4 Myr post-MS isochrone. The age of the optically selected PMS population is estimated to be 7-8 Myr. The IR-excess population shows sub-clustering on scales as small as 0.23 pc and is probably much younger.Comment: 15 pages, 16 figure

Enumeration of Standard Young Tableaux

A survey paper, to appear as a chapter in a forthcoming Handbook on Enumeration.Comment: 65 pages, small correction

Different Evolutionary Stages in the Massive Star Forming Region S255 Complex

To understand evolutionary and environmental effects during the formation of high-mass stars, we observed three regions of massive star formation at different evolutionary stages that reside in the same natal molecular cloud. Methods. The three regions S255IR, S255N and S255S were observed at 1.3 mm with the Submillimeter Array (SMA) and followup short spacing information was obtained with the IRAM 30m telescope. Near infrared (NIR) H + K-band spectra and continuum observations were taken for S255IR with VLT-SINFONI to study the different stellar populations in this region. The combination of millimeter (mm) and near infrared data allow us to characterize different stellar populations within the young forming cluster in detail. While we find multiple mm continuum sources toward all regions, their outflow, disk and chemical properties vary considerably. The most evolved source S255IR exhibits a collimated bipolar outflow visible in CO and H2 emission, the outflows from the youngest region S255S are still small and rather confined in the regions of the mm continuum peaks. Also the chemistry toward S255IR is most evolved exhibiting strong emission from complex molecules, while much fewer molecular lines are detected in S255N, and in S255S we detect only CO isotopologues and SO lines. Also, rotational structures are found toward S255N and S255IR. Furthermore, a comparison of the NIR SINFONI and mm data from S255IR clearly reveal two different (proto) stellar populations with an estimated age difference of approximately 1 Myr. A multi-wavelength spectroscopy and mapping study reveals different evolutionary phases of the star formation regions. We propose the triggered outside-in collapse star formation scenario for the bigger picture and the fragmentation scenario for S255IR.Comment: 23 pages,25 figures, accepted by A&

Different Evolutionary Stages in the Massive Star Forming Region W3 Main Complex

We observed three high-mass star-forming regions in the W3 high-mass star formation complex with the Submillimeter Array and IRAM 30 m telescope. These regions, i.e. W3 SMS1 (W3 IRS5), SMS2 (W3 IRS4) and SMS3, are in different evolutionary stages and are located within the same large-scale environment, which allows us to study rotation and outflows as well as chemical properties in an evolutionary sense. While we find multiple mm continuum sources toward all regions, these three sub-regions exhibit different dynamical and chemical properties, which indicates that they are in different evolutionary stages. Even within each subregion, massive cores of different ages are found, e.g. in SMS2, sub-sources from the most evolved UCHII region to potential starless cores exist within 30 000 AU of each other. Outflows and rotational structures are found in SMS1 and SMS2. Evidence for interactions between the molecular cloud and the HII regions is found in the 13CO channel maps, which may indicate triggered star formation.Comment: Accepted for publication in ApJ, 22 pages, 23 figure

Dynamical structure of the inner 100 AU of the deeply embedded protostar IRAS 16293-2422

A fundamental question about the early evolution of low-mass protostars is when circumstellar disks may form. High angular resolution observations of molecular transitions in the (sub)millimeter wavelength windows make it possible to investigate the kinematics of the gas around newly-formed stars, for example to identify the presence of rotation and infall. IRAS 16293-2422 was observed with the extended Submillimeter Array (eSMA) resulting in subarcsecond resolution (0.46" x 0.29", i.e. $\sim$ 55 $\times$ 35~AU) images of compact emission from the C$^{17}$O (3-2) and C$^{34}$S (7-6) transitions at 337~GHz (0.89~mm). To recover the more extended emission we have combined the eSMA data with SMA observations of the same molecules. The emission of C$^{17}$O (3-2) and C$^{34}$S (7-6) both show a velocity gradient oriented along a northeast-southwest direction with respect to the continuum marking the location of one of the components of the binary, IRAS16293A. Our combined eSMA and SMA observations show that the velocity field on the 50--400~AU scales is consistent with a rotating structure. It cannot be explained by simple Keplerian rotation around a single point mass but rather needs to take into account the enclosed envelope mass at the radii where the observed lines are excited. We suggest that IRAS 16293-2422 could be among the best candidates to observe a pseudo-disk with future high angular resolution observations.Comment: Accepted for publication in ApJ, 18 pages, 10 figure

The high-mass disk candidates NGC7538IRS1 and NGC7538S

Context: The nature of embedded accretion disks around forming high-mass stars is one of the missing puzzle pieces for a general understanding of the formation of the most massive and luminous stars. Methods: Using the Plateau de Bure Interferometer at 1.36mm wavelengths in its most extended configuration we probe the dust and gas emission at ~0.3",corresponding to linear resolution elements of ~800AU. Results: NGC7538IRS1 remains a single compact and massive gas core with extraordinarily high column densities, corresponding to visual extinctions on the order of 10^5mag, and average densities within the central 2000AU of ~2.1x10^9cm^-3 that have not been measured before. We identify a velocity gradient across in northeast-southwest direction that is consistent with the mid-infrared emission, but we do not find a gradient that corresponds to the proposed CH3OH maser disk. The spectral line data toward NGC7538IRS1 reveal strong blue- and red-shifted absorption toward the mm continuum peak position. The red-shifted absorption allows us to estimate high infall rates on the order of 10^-2 Msun/yr. Although we cannot prove that the gas will be accreted in the end, the data are consistent with ongoing star formation activity in a scaled-up low-mass star formation scenario. Compared to that, NGC7538S fragments in a hierarchical fashion into several sub-sources. While the kinematics of the main mm peak are dominated by the accompanying jet, we find rotational signatures from a secondary peak. Furthermore, strong spectral line differences exist between the sub-sources which is indicative of different evolutionary stages within the same large-scale gas clump.Comment: 15 pages, 12 figures, accepted for A&

The pillowcase distribution and near-involutions

In the context of the Eskin-Okounkov approach to the calculation of the volumes of the different strata of the moduli space of quadratic differentials, the important ingredients are the pillowcase weight probability distribution on the space of Young diagrams, and the asymptotic study of characters of permutations that near-involutions. In this paper we present various new results for these objects. Our results give light to unforeseen difficulties in the general solution to the problem, and they simplify some of the previous proofs.Comment: This paper elaborates on some of the results of the author's PhD thesis (arXiv:1209.4333). This is the published version, http://ejp.ejpecp.org/article/view/362