A study on subarcsecond scales of the ammonia and continuum emission toward the G16.59-0.05 high-mass star-forming region

We wish to investigate the structure, velocity field, and stellar content of the G16.59-0.05 high-mass star-forming region, where previous studies have established the presence of two almost perpendicular (NE-SW and SE-NW), massive outflows, and a rotating disk traced by methanol maser emission. We performed Very Large Array observations of the radio continuum and ammonia line emission, complemented by COMICS/Subaru and Hi-GAL/Herschel images in the mid- and far-infrared (IR). Our centimeter continuum maps reveal a collimated radio jet that is oriented E-W and centered on the methanol maser disk, placed at the SE border of a compact molecular core. The spectral index of the jet is negative, indicating non-thermal emission over most of the jet, except the peak close to the maser disk, where thermal free-free emission is observed. We find that the ammonia emission presents a bipolar structure consistent (on a smaller scale) in direction and velocity with that of the NE-SW bipolar outflow detected in previous CO observations. After analyzing our previous N2H+(1-0) observations again, we conclude that two scenarios are possible. In one case both the radio jet and the ammonia emission would trace the root of the large-scale CO bipolar outflow. The different orientation of the jet and the ammonia flow could be explained by precession and/or a non-isotropic density distribution around the star. In the other case, the N2H+(1-0) and ammonia bipolarity is interpreted as two overlapping clumps moving with different velocities along the line of sight. The ammonia gas also seems to undergo rotation consistent with the maser disk. Our IR images complemented by archival data allow us to derive a bolometric luminosity of about 10^4 L_sun and to conclude that most of the luminosity is due to the young stellar object associated with the maser disk.Comment: 11 pages, 12 figures, published in Astronomy and Astrophysic

Evolution and excitation conditions of outflows in high-mass star-forming regions

Theoretical models suggest that massive stars form via disk-mediated accretion, with bipolar outflows playing a fundamental role. A recent study toward massive molecular outflows has revealed a decrease of the SiO line intensity as the object evolves. The present study aims at characterizing the variation of the molecular outflow properties with time, and at studying the SiO excitation conditions in outflows associated with massive YSOs. We used the IRAM30m telescope to map 14 massive star-forming regions in the SiO(2-1), SiO(5-4) and HCO+(1-0) outflow lines, and in several dense gas and hot core tracers. Hi-GAL data was used to improve the spectral energy distributions and the L/M ratio, which is believed to be a good indicator of the evolutionary stage of the YSO. We detect SiO and HCO+ outflow emission in all the sources, and bipolar structures in six of them. The outflow parameters are similar to those found toward other massive YSOs. We find an increase of the HCO+ outflow energetics as the object evolve, and a decrease of the SiO abundance with time, from 10^(-8) to 10^(-9). The SiO(5-4) to (2-1) line ratio is found to be low at the ambient gas velocity, and increases as we move to high velocities, indicating that the excitation conditions of the SiO change with the velocity of the gas (with larger densities and/or temperatures for the high-velocity gas component). The properties of the SiO and HCO+ outflow emission suggest a scenario in which SiO is largely enhanced in the first evolutionary stages, probably due to strong shocks produced by the protostellar jet. As the object evolves, the power of the jet would decrease and so does the SiO abundance. During this process, however, the material surrounding the protostar would have been been swept up by the jet, and the outflow activity, traced by entrained molecular material (HCO+), would increase with time.Comment: 31 pages, 10 figures and 5 tables (plus 2 figures and 3 tables in the appendix). Accepted for publication in A&A. [Abstract modified to fit the arXiv requirements.

Probing the initial conditions of high-mass star formation -- IV. Gas dynamics and NH2_2D chemistry in high-mass precluster and protocluster clumps

The initial stage of star formation is a complex area study because of its high density and low temperature. Under such conditions, many molecules become depleted from the gas phase by freezing out onto dust grains. However, the deuterated species could remain gaseous and are thus ideal tracers. We investigate the gas dynamics and NH$_2$D chemistry in eight massive pre/protocluster clumps. We present NH$_2$D 1$_{11}$-1$_{01}$ (at 85.926 GHz), NH$_3$ (1, 1) and (2, 2) observations in the eight clumps using the PdBI and the VLA, respectively. We find that the distribution between deuterium fractionation and kinetic temperature shows a number density peak at around $T_{\rm kin}=16.1$ K, and the NH$_2$D cores are mainly located at a temperature range of 13.0 to 22.0 K. We detect seven instances of extremely high deuterium fractionation of $1.0 \leqslant D_{\rm frac} \leqslant 1.41$. We find that the NH$_2$D emission does not appear to coincide exactly with either dust continuum or NH$_3$ peak positions, but often surrounds the star-formation active regions. This suggests that the NH$_{2}$D has been destroyed by the central young stellar object (YSO) due to its heating. The detected NH$_2$D lines are very narrow with a median width of $\rm 0.98\pm0.02 km/s$. The extracted NH$_2$D cores are gravitationally bound ($\alpha_{\rm vir} < 1$), are likely prestellar or starless, and can potentially form intermediate-mass or high-mass stars. Using NH$_3$ (1, 1) as a dynamical tracer, we find very complicated dynamical movement, which can be explained by a combined process with outflow, rotation, convergent flow, collision, large velocity gradient, and rotating toroids. High deuterium fractionation strongly depends on the temperature condition. NH$_2$D is a poor evolutionary indicator of high-mass star formation in evolved stages, but a useful tracer in the starless and prestellar cores.Comment: 27 pages, 25 figures, 6 tables, accepted for publication in A&

A differentially rotating disc in a high-mass protostellar system

A strong signature of a circumstellar disc around a high-mass protostar has been inferred from high resolution methanol maser observations in NGC7538-IRS1 N. This interpretation has however been challenged with a bipolar outflow proposed as an alternative explanation. We compare the two proposed scenarios for best consistency with the observations. Using a newly developed formalism we model the optical depth of the maser emission at each observed point in the map and LOS velocity for the two scenarios. We find that if the emission is symmetric around a central peak in both space and LOS velocity then it has to arise from an edge-on disc in sufficiently fast differential rotation. Disc models successfully fit ~100 independent measurement points in position-velocity space with 4 free parameters to an overall accuracy of 3-4%. Solutions for Keplerian rotation require a central mass of at least 4 solar masses. Close to best-fitting models are obtained if Keplerian motion is assumed around a central mass equaling ~30 solar masses as inferred from other observations. In contrast we find that classical bipolar outflow models cannot fit the data, although could be applicable in other sources. Our results strongly favour the differentially rotating disc hypothesis to describe the main feature of the 12.2 (and 6.7) GHz methanol maser emission in NGC7538 IRS1 N. Furthermore, for Keplerian rotation around a ~30 solar masses protostar we predict the position and velocity at which tangentially amplified masers should be detected in high dynamic range observations. [abridged]Comment: 13 pages, 11 figures, accepted for publication in A&

NG7538 IRS1 N: modeling a circumstellar maser disk

We present an edge-on Keplerian disk model to explain the main component of the 12.2 and 6.7 GHz methanol maser emission detected toward NGC7538-IRS1 N. The brightness distribution and spectrum of the line of bright masers are successfully modeled with high amplification of background radio continuum emission along velocity coherent paths through a maser disk. The bend seen in the position-velocity diagram is a characteristic signature of differentially rotating disks. For a central mass of 30 solar masses, suggested by other observations, our model fixes the masing disk to have inner and outer radii of about 270 AU and 750 AU.Comment: To appear in The Proceedings of the 2004 European Workshop: "Dense Molecular Gas around Protostars and in Galatic Nuclei", Eds. Y. Hagiwara, W.A. Baan, H.J. van Langevelde, 2004, a special issue of ApSS, Kluwe

Radio emission from the high-mass X-ray binary BP Cru: first detection

BP Cru is a well known high-mass X-ray binary composed of a late B hypergiant (Wray 977) and a neutron star, also observed as the X-ray pulsar GX 301-2. No information about emission from BP Cru in other bands than X-rays and optical has been reported to date in the literature, though massive X-ray binaries containing black holes can have radio emission from a jet. In order to assess the presence of a radio jet, we searched for radio emission towards BP Cru using the Australia Compact Array Telescope during a survey for radio emission from Be/X-ray transients. We probed the 41.5d orbit of BP Cru with the Australia Telescope Compact Array not only close to periastron but also close to apastron. BP Cru was clearly detected in our data on 4, possibly 6, of 12 occasions at 4.8 and 8.6 GHz. Our data suggest that the spectral index of the radio emission is modulated either by the X-ray flux or the orbital phase of the system. We propose that the radio emission of BP Cru probably arises from two components: a persistent component, coming from the mass donor Wray 977, and a periodic component connected to the accretion onto the neutron star, possibly coming from a (weak and short lived) jet.Comment: 2 figures, accepted for publication in A+A letter

Bipolar HII regions - Morphology and star formation in their vicinity - I - G319.88++00.79 and G010.32−-00.15

Our goal is to identify bipolar HII regions and to understand their morphology, their evolution, and the role they play in the formation of new generations of stars. We use the Spitzer and Herschel Hi-GAL surveys to identify bipolar HII regions. We search for their exciting star(s) and estimate their distances using near-IR data. Dense clumps are detected using Herschel-SPIRE data. MALT90 observations allow us to ascertain their association with the central HII region. We identify Class 0/I YSOs using their Spitzer and Herschel-PACS emissions. These methods will be applied to the entire sample of candidate bipolar HII regions. This paper focuses on two bipolar HII regions, one interesting in terms of its morphology, G319.88$+$00.79, and one in terms of its star formation, G010.32$-$00.15. Their exciting clusters are identified and their photometric distances estimated to be 2.6 kpc and 1.75 kpc, respectively. We suggest that these regions formed in dense and flat structures that contain filaments. They have a central ionized region and ionized lobes perpendicular to the parental cloud. The remains of the parental cloud appear as dense (more than 10^4 per cm^3) and cold (14-17 K) condensations. The dust in the PDR is warm (19-25 K). Dense massive clumps are present around the central ionized region. G010.32-00.14 is especially remarkable because five clumps of several hundred solar masses surround the central HII region; their peak column density is a few 10^23 per cm^2, and the mean density in their central regions reaches several 10^5 per cm^3. Four of them contain at least one massive YSO; these clumps also contain extended green objects and Class II methanol masers. This morphology suggests that the formation of a second generation of massive stars has been triggered by the central bipolar HII region. It occurs in the compressed material of the parental cloud.Comment: 32 pages, 28 figures, to be published in A&

The impact of adding low-dose leucovorin to monthly 5-fluorouracil in advanced colorectal carcinoma: Results of a phase III trial

Purpose A wide variety of fiuorouracil (FU)-plus-leucovorin (LV) dose schedules are in clinical use for the treatment of advanced colorectal cancer. Only the monthly low-dose LV-plus-FU regimen, as used by the North Central Cancer Treatment Group, has demonstrated a lasting survival benefit as opposed to FU alone (J Clin Oncol 1989; 7: 1407-1417). The Swiss Cancer Group adopted this regimen for a confirmatory phase III trial but used the same dose-intensity of fiuorouracil in both treatment arms. Patients and methods Patients with inoperable or metastatic colorectal cancer were randomized to receive monthly FU 400 mg/m2/day plus LV 20 mg/m2/day as intravenous push daily for five days, or FU alone. Results Three hundred nine of the 310 patients randomized were eligible and included in the analysis. The objective response rate for patients with measurable disease was 9% with FU alone and 22% with FU-plus-LV (P= 0.0001). The median progression-free survival was 3.9 versus 6.2 months (P = 0.003) and the overall survival 10 versus 12.4 months (P = 0.02). The major prognostic factors for survival were performance status, weight loss, and disease symptoms. WHO > 2 toxicity, consisting of stomatitis (P = 0.001), diarrhea (P=0.001), and nausea (P), = 0.001), was more pronounced for FU-plus-LV, without fatal events. Conclusions This is the largest published randomized trial to compare FU-plus-LV to FU alone in advanced colorectal cancer. It confirms the survival benefit obtained from biomo-dulating monthly FU with low-dose LV. The toxic effects of FU-plus-LV were acceptable to most patients, and they responded well to FU dose reductions. In the absence of an ideal dose-intense FU monotherapy regimen, monthly FU with low-dose LV provides a simple and economical means by which to achieve adequate FU efficacy in the treatment of advanced colorectal cance