Herbig-Haro flows in L1641N

We have used the 2.56m Nordic Optical Telescope (NOT) to observe two deep fields in L1641N, selected on the basis of previous shock studies, using the 2.12 micron transition of H2 (and a Ks filter to sample the continuum) for a total exposure time of 4.6 h (72 min Ks) in the overlapping region. The resulting high-resolution mosaic shows numerous new shocks and resolves many known shocks into multiple components. Using previous observations taken 9 years earlier we calculate a proper motion map and combine this with Spitzer 24 micron observations of the embedded young stars. The combined H2 mosaic shows many new shocks and faint structures in the HH flows. From the proper motion map we find that most HH objects belong to two major bi-polar HH flows, the large-scale roughly North-South oriented flow from central L1641N and a previously unseen HH flow in eastern L1641N. Combining the tangential velocity map with the mid-IR Spitzer images, two very likely outflow sources are found. The outflow source of the eastern flow, L1641N-172, is found to be the currently brightest mid-IR source in L1641N and seem to have brightened considerably during the past 20 years. We make the first detection of this source in the near-IR (Ks) and also find a near-IR reflection nebula pointing at the source, probably the illuminated walls of a cone-shaped cavity cleared out by the eastern lobe of the outflow. Extending a line from the eastern outflow source along the proper motion vector we find that HH 301 and HH 302 (almost 1 pc away) belong to this new HH flow.Comment: 10 pages, 4 figures, Accepted for publication by A &

Herbig-Haro flows in B335

We have observed optical (Halpha and [SII]) and near-IR (S(1) line of H2) deep fields and taken optical spectra using the 2.56m NOT, as well as a near-UV deep field (U band) using the 3.58m NTT. In addition we present new SPITZER (IRAC and MIPS) mid-IR observations. We use previous Halpha and S(1) observations taken 15 and 9 years earlier to make proper motion maps. We then investigate the shock physics by matching our spectra with planar shock models. We discover six new HH objects in B335. From proper motions we find an optically bright, roughly E-W oriented group with high space velocities (200-280 km/s) and a near-IR bright, slower group (15-75 km/s) moving to the ESE. We also find a system of at least 15 H2 knots in the western lobe. This (WNW) counterflow suggests the possibility of a binary outflow source, giving rise to two outflow axes with slightly different orientations. We find that the E-W flow is symmetrical with evidence for two outbursts. We make the first detection of [OI] 6300/63 in HH119 B and Hbeta in HH119 A and B and find their extinctions to be AV~1.4 and 4.4, respectively. HH119 A is found to expand much faster than expected from linear expansion with distance from the outflow source. Using planar shock models we find shock velocities of ~60 km/s (A) and ~35 km/s (B and C). This agrees with A being of higher excitation than B and C. In our U image we detect three of the HH objects and propose that the emission arise from the [OII] 3728 line and the blue continuum. New SPITZER observations show most of the HH objects at 4.5 micron and a E-W elongated hour-glass shaped structure at the outflow source. Even at 24 micron it is not clear whether most of the light is direct or reflected.Comment: 23 pages, 15 figures, accepted in A&

ISOCAM observations of the L1551 star formation region

The results of a deep mid-IR ISOCAM survey of the L1551 dark molecular cloud are presented. The aim of this survey is a search for new YSO (Young Stellar Object) candidates, using two broad-band filters centred at 6.7 and 14.3 micron. Although two regions close to the centre of L1551 had to be avoided due to saturation problems, 96 sources were detected in total (76 sources at 6.7 micron and 44 sources at 14.3 micron). Using the 24 sources detected in both filters, 14 were found to have intrinsic mid-IR excess at 14.3 micron and were therefore classified as YSO candidates. Using additional observations in B, V, I, J, H and K obtained from the ground, most candidates detected at these wavelengths were confirmed to have mid-IR excess at 6.7 micron as well, and three additional YSO candidates were found. Prior to this survey only three YSOs were known in the observed region (avoiding L1551 IRS5/NE and HL/XZ Tau). This survey reveals 15 new YSO candidates, although several of these are uncertain due to their extended nature either in the mid-IR or in the optical/near-IR observations. Two of the sources with mid-IR excess are previously known YSOs, one is a brown dwarf MHO 5 and the other is the well known T Tauri star HH30, consisting of an outflow and an optically thick disk seen edge on.Comment: 14 Pages, 8 Figure

A multi-wavelength census of star formation activity in the young embedded cluster around Serpens/G3-G6

Aims. The aim of this paper is to characterise the star formation activity in the poorly studied embedded cluster Serpens/G3-G6, located ~ 45' (3 pc) to the south of the Serpens Cloud Core, and to determine the luminosity and mass functions of its population of Young Stellar Objects (YSOs). Methods. Multi-wavelength broadband photometry was obtained to sample the near and mid-IR spectral energy distributions to separate YSOs from field stars and classify the YSO evolutionary stage. ISOCAM mapping in the two filters LW2 (5-8.5 um) and LW3 (12-18 um) of a 19' x 16' field was combined with JHKs data from 2MASS, Ks data from Arnica/NOT, and L' data from SIRCA/NOT. Continuum emission at 1.3 mm (IRAM) and 3.6 cm (VLA) was mapped to study the cloud structure and the coldest/youngest sources. Deep narrow band imaging at the 2.12 um S(1) line of H2 from NOTCam/NOT was obtained to search for signs of bipolar outflows. Results. We have strong evidence for a stellar population of 31 Class II sources, 5 flat-spectrum sources, 5 Class I sources, and two Class 0 sources. Our method does not sample the Class III sources. The cloud is composed of two main dense clumps aligned along a ridge over ~ 0.5 pc plus a starless core coinciding with absorption features seen in the ISOCAM maps. We find two S-shaped bipolar collimated flows embedded in the NE clump, and propose the two driving sources to be a Class 0 candidate (MMS3) and a double Class I (MMS2). For the Class II population we find a best age of ~ 2 Myr and compatibility with recent Initial Mass Functions (IMFs) by comparing the observed Class II luminosity function (LF), which is complete to 0.08 L_sun, to various model LFs with different star formation scenarios and input IMFs.Comment: 18 pages, 16 figures, 3 online tables, accepted by A&

A General Catalogue of Molecular Hydrogen Emission-Line Objects (MHOs) in Outflows from Young Stars

We present a catalogue of Molecular Hydrogen emission-line Objects (MHOs) in outflows from young stars, most of which are embedded. All objects are identified in the near-infrared lines of molecular hydrogen, all reside in the Milky Way, and all are associated with jets or molecular outflows from young stars. Objects in both low and high-mass star forming regions are included. This catalogue complements the existing database of Herbig-Haro objects; indeed, for completeness, HH objects that are detected in H2 emission are included in the MHO catalogue.Comment: 8 Pages, 5 figures. Accepted for publication in A&A. Searchable catalogue/Data tables available from http://www.jach.hawaii.edu/UKIRT/MHCat

Management Effects on Greenhouse Gas Dynamics in Fen Ditches

Globally, large areas of peatland have been drained through the digging of ditches, generally to increase agricultural production. By lowering the water table it is often assumed that drainage reduces landscape-scale emissions of methane (CH4) into the atmosphere to negligible levels. However, drainage ditches themselves are known to be sources of CH4 and other greenhouse gases (GHGs), but emissions data are scarce, particularly for carbon dioxide (CO2) and nitrous oxide (N2O), and show high spatial and temporal variability. Here, we report dissolved GHGs and diffusive fluxes of CH4 and CO2 from ditches at three UK lowland fens under different management; semi-natural fen, cropland, and cropland restored to low-intensity grassland. Ditches at all three fens emitted GHGs to the atmosphere, but both fluxes and dissolved GHGs showed extensive variation both seasonally and within-site. CH4 fluxes were particularly large, with medians peaking at all three sites in August at 120-230 mg m-2 d-1. Significant between site differences were detected between the cropland and the other two sites for CO2 flux and all three dissolved GHGs, suggested that intensive agriculture has major effects on ditch biogeochemistry. Multiple regression models using environmental and water chemistry data were able to explain 29-59% of observed variation in dissolved GHGs. Annual CH4 fluxes from the ditches were 37.8, 18.3 and 27.2 g CH4 m-2 yr-1 for the semi-natural, grassland and cropland, and annual CO2 fluxes were similar (1100 to 1440 g CO2 m-2 yr-1) among sites. We suggest that fen ditches are important contributors to landscape-scale GHG emissions, particularly for CH4. Ditch emissions should be included in GHG budgets of human modified fens, particularly where drainage has removed the original terrestrial CH4 source, e.g. agricultural peatlands

Odin observations of water in molecular outflows and shocks

Aims. We investigate the ortho-water abundance in outflows and shocks in order to improve our knowledge of shock chemistry and of the physics behind molecular outflows. Methods. We have used the Odin space observatory to observe the H2O(110-101) line. We obtain strip maps and single pointings of 13 outflows and two supernova remnants where we report detections for eight sources. We have used RADEX to compute the beam averaged abundances of o-H2O relative to H2. In the case of non-detection, we derive upper limits on the abundance. Results. Observations of CO emission from the literature show that the volume density of H2 can vary to a large extent, a parameter that puts severe uncertainties on the derived abundances. Our analysis shows a wide range of abundances reflecting the degree to which shock chemistry is affecting the formation and destruction of water. We also compare our results with recent results from the SWAS team. Conclusions. Elevated abundances of ortho-water are found in several sources. The abundance reaches values as high as what would be expected from a theoretical C-type shock where all oxygen, not in the form of CO, is converted to water. However, the high abundances we derive could also be due to the low densities (derived from CO observations) that we assume. The water emission may in reality stem from high density regions much smaller than the Odin beam. We do not find any relationship between the abundance and the mass loss rate. On the other hand, there is a relation between the derived water abundance and the observed maximum outflow velocity.Comment: 19 pages, 20 figures, 4 table

The afterglows of Swift-era gamma-ray bursts. I. Comparing pre-Swift and Swift-era long/soft (type II) GRB optical afterglows

We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical highluminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A

A detailed study of the L1641N star formation region

Aims. We search for young stellar objects (YSOs) in the L1641N cluster and characterize the star formation activity through determination of the age distribution, mass function, spatial distribution, and the star formation history. Methods. Multi-wavelength broad band photometry both from space and the ground are used to look for IR excess in order to separate field stars from YSOs and to sample the spectral energy distributions. Space-based observations were obtained using the ISO satellite (ISOCAM) in two filters, centred at 6.7 and 14.3 μm, and Spitzer (IRAC) at 3.6, 4.5, 5.8, and 8.0 μm. Our ground-based observations were made with the Nordic Optical Telescope (NOT) using ALFOSC (I band), NOTCam (J, KS and 2.12 μm H2), and SIRCA (L'). More than 50 of the brightest I-band sources were then studied with follow-up optical spectroscopy (5780-8340 Å) to check for signs of accretion (Hα in emission) and youth (Li I $\lambda6707$ in absorption) and to determine their effective temperatures. By comparing theoretical evolution tracks with our YSO sample in the H-R diagram, we calculated an age, luminosity, and mass distribution. Results. We detect a total of 216 (Spitzer or I band) sources in L1641N, 89 of which are YSO candidates. Most of the spectra are of M-type with Hα strongly in emission, and many have Li 6707 in absorption. The four brightest I band sources (F and G stars) are suggested as foreground stars, and the L1641N IRAS source is shown to be the combined flux of at least four sources. We find that the interstellar extinction is well-fit in the optical and near-IR by a power law with an exponent of 1.58, although in the mid-IR the Spitzer observations show a higher extinction than expected from theory. The median age of the YSO sample is ~1 Myr and the resulting MF has a flat distribution for low masses down to the completeness limit. There is evidence of a constant star formation rate of one star in 3.7 $\times$ 104 yr during the past few Myr. We find 11 sources older than 10 Myr and a spatial separation between younger and older YSOs, suggesting that many of the older stars formed in L1641N could have left the cluster, giving the appearance of an increased star formation rate with time

Herbig-Haro flows in

Aims.To study the Herbig-Haro (HH) flows in L1641