Ionized Gas Kinematics and Morphology in Sgr B2 Main on 1000 AU Scales

We have imaged the Sgr B2 Main region with the Very Large Array in the BnA configuration ($\theta_{beam}$ = 0\farcs13) in both the H52$\alpha$ (45.453 GHz) radio recombination line (RRL) and 7 mm continuum emission. At a distance of 8500 pc, this spatial resolution corresponds to a physical scale of 0.005 pc ($\sim$1100 AU). The current observations detect H52$\alpha$ emission in 12 individual ultracompact (UC) and hypercompact (HC) HII regions. Two of the sources with detected H52 $\alpha$ emission have broad ($\Delta$V$_{FWHM}\sim$50 \kms) recombination lines, and two of the sources show lines with peaks at more than one velocity. We use line parameters from the H52$\alpha$ lines and our previous H66$\alpha$ line observations to determine the relative contribution of thermal, pressure and kinematic broadening, and electron density. These new observations suggest that pressure broadening can account for the broad lines in some of the sources, but that gas motions (e.g. turbulence, accretion or outflow) contribute significantly to the broad lines in at least one of the sources (Sgr B2 F3).Comment: 10 pages, 2 figure

WSRT and VLA Observations of the 6 cm and 2 cm lines of H2CO in the direction of W 58 C1(ON3) and W 58 C2

Absorption in the J{K-K+} = 2{11}-2{12} transition of formaldehyde at 2 cm towards the ultracompact HII regions C1 and C2 of W 58 has been observed with the VLA with an angular resolution of ~0.2'' and a velocity resolution of ~1 km/s. The high resolution continuum image of C1 (ON 3) shows a partial shell which opens to the NE. Strong H2CO absorption is observed against W 58 C1. The highest optical depth (tau > 2) occurs in the SW portion of C1 near the edge of the shell, close to the continuum peak. The absorption is weaker towards the nearby, more diffuse compact HII region C2, tau<~0.3. The H2CO velocity (-21.2 km/s) towards C1 is constant and agrees with the velocity of CO emission, mainline OH masers, and the H76 alpha recombination line, but differs from the velocity of the 1720 MHz OH maser emission (~-13 km/s). Observations of the absorption in the J{K-K+} = 1{10}-1{11} transition of formaldehyde at 6 cm towards W 58 C1 and C2 carried out earlier with the WSRT at lower resolution (~4''x7'') show comparable optical depths and velocities to those observed at 2 cm. Based on the mean optical depth profiles at 6 cm and 2 cm, the volume density of molecular hydrogen n(H2) and the formaldehyde column density N(H2CO) were determined. The n(H2) is ~6E4 /cm**3 towards C1. N(H2CO) for C1 is ~8E14 /cm**2 while that towards C2 is ~8E13 /cm**2.Comment: AJ in press Jan 2001, 14 pages plus 6 figures (but Fig. 1 has 4 separate parts, a through d). Data are available at http://adil.ncsa.uiuc.edu/document/00.HD.0

Multiwavelength Observations of Massive Stellar Cluster Candidates in the Galaxy

The Galaxy appears to be richer in young, massive stellar clusters than previously known, due to advances in infrared surveys which have uncovered deeply embedded regions of star formation. Young, massive clusters can significantly impact the surrounding interstellar medium (ISM) and hence radio observations can also be an important tracer of their activity. Several hundred cluster candidates are now known by examining survey data. Here we report on multiwavelength observations of six of these candidates in the Galaxy. We carried out 4.9 and 8.5 GHz VLA observations of the radio emission associated with these clusters to obtain the physical characteristics of the surrounding gas, including the Lyman continuum photon flux and ionized gas mass. Spitzer Infrared Array Camera observations were also made of these regions, and provide details on the stellar population as well as the dust continuum and polycyclic aromatic hydrocarbon emission. When compared to the known young, massive clusters in the Galaxy, the six cluster candidates have less powerful Lyman ionizing fluxes and ionize less of the H II mass in the surrounding ISM. Therefore, these cluster candidates appear to be more consistent with intermediate-mass clusters (10^3-10^4 Msun).Comment: 39 pages, 20 figures. Accepted in the Astronomical Journal; to be published Fall 201

VLA observations of candidate high-mass protostellar objects at 7 mm

We present radio continuum observations at 7 mm made using the Very Large Array towards three massive star forming regions thought to be in very early stages of evolution selected from the sample of Sridharan et al. (2002). Emission was detected towards all three sources (IRAS 18470-0044, IRAS 19217+1651 and IRAS 23151+5912). We find that in all cases the 7 mm emission corresponds to thermal emission from ionized gas. The regions of ionized gas associated with IRAS 19217+1651 and IRAS 23151+5912 are hypercompact with diameters of 0.009 and 0.0006 pc, and emission measures of 7.0 x 10^8 and 2.3 x 10^9 pc cm^(-6), respectively.Comment: 17 pages, 5 figures, accepted by The Astronomical Journa

A randomized double-blind trial to compare the clinical efficacy of granisetron with metoclopramide, both combined with dexamethasone in the prophylaxis of chemotherapy-induced delayed emesis

Background: The prophylactic use of 5-HT3 receptor antagonists (setrons), after the first 24 h (acute phase) of exposure to emetic chemotherapy, to decrease the incidence of ‘delayed phase' emesis increases costs. We designed a study to evaluate the efficacy of a setron (granisetron) in the delayed phase, compared with metoclopramide, each combined with a corticosteroid. Patients and methods: Patients on their first course of single-day emetic chemotherapy (cisplatin, carboplatin, doxorubicin, cyclophosphamide and others) received granisetron 2 mg p.o. and dexamethasone 8 mg p.o. on day 1, followed for 5 days by dexamethasone 4 mg p.o. od combined with either metoclopramide 20 mg p.o. tds or granisetron 1 mg bd in a double-blinded double-dummy protocol. Patients evaluated the results using a diary card. Randomization was stratified by institution, sex, emetic chemotherapy naïve versus previous, alcohol consumption and platinum versus non-platinum regimen. Results: 131 evaluable patients received granisetron in the delayed phase, and 127 received metoclopramide. Control of acute emesis in both arms was similar (86% granisetron; 85% metoclopramide). The 35 patients experiencing acute emesis had poor control in the delayed phase, with only four granisetron and three metoclopramide patients having no or mild nausea and no vomiting. Conclusions: In daily practice, a combination of oral dexamethasone and oral granisetron achieves an extremely high control of acute emesis (86% protection). Our data suggest that routine prescription of setrons for delayed phase control is not advisable as it increases costs without any benefit for the majority of patients. Delayed emesis in the rare patients with acute phase emesis remains an unsolved proble

W49A: A starburst triggered by expanding shells

W49A is a giant molecular cloud which harbors some of the most luminous embedded clusters in the Galaxy. However, the explanation for this starburst-like phenomenon is still under debate. Methods. We investigated large-scale Spitzer mid-infrared images together with a Galatic Ring Survey 13CO J = 1-0 image, complemented with higher resolution (~ 11 arcsec) 13CO J = 2-1 and C18O J = 2-1 images over a ~ 15 x 13 pc^2 field obtained with the IRAM 30m telescope. Two expanding shells have been identified in the mid-infrared images, and confirmed in the position-velocity diagrams made from the 13CO J = 2-1 and C18O J = 2-1 data. The mass of the averaged expanding shell, which has an inner radius of ~ 3.3 pc and a thickness of ~ 0.41 pc, is about 1.9 x 10^4 M*. The total kinetic energy of the expanding shells is estimated to be ~ 10^49 erg which is probably provided by a few massive stars, whose radiation pressure and/or strong stellar winds drive the shells. The expanding shells are likely to have a common origin close to the two ultracompact Hii regions (source O and source N), and their expansion speed is estimated to be ~ 5 km/s, resulting in an age of ~ 3-7 x 10^5 years. In addition, on larger (~ 35 x 50 pc^2) scales, remnants of two gas ejections have been identified in the 13CO J = 1 - 0 data. Both ejections seem to have the same center as the expanding shells with a total energy of a few times 10^50 erg. The main driving mechanism for the gas ejections is unclear, but likely related to the mechanism which triggers the starburst in W49A

Flickering of 1.3 cm Sources in Sgr B2: Towards a Solution to the Ultracompact HII Region Lifetime Problem

Accretion flows onto massive stars must transfer mass so quickly that they are themselves gravitationally unstable, forming dense clumps and filaments. These density perturbations interact with young massive stars, emitting ionizing radiation, alternately exposing and confining their HII regions. As a result, the HII regions are predicted to flicker in flux density over periods of decades to centuries rather than increasing monotonically in size as predicted by simple Spitzer solutions. We have recently observed the Sgr B2 region at 1.3 cm with the VLA in its three hybrid configurations (DnC, CnB and BnA) at a resolution of 0.25''. These observations were made to compare in detail with matched continuum observations from 1989. At 0.25'' resolution, Sgr B2 contains 41 UC HII regions, 6 of which are hypercompact. The new observations of Sgr B2 allow comparison of relative peak flux densites for the HII regions in Sgr B2 over a 23 year time baseline (1989-2012) in one of the most source-rich massive star forming regions in the Milky Way. The new 1.3 cm continuum images indicate that four of the 41 UC HII regions exhibit significant changes in their peak flux density, with one source (K3) dropping in peak flux density, and the other 3 sources (F10.303, F1 and F3) increasing in peak flux density. The results are consistent with statistical predictions from simulations of high mass star formation, suggesting that they offer a solution to the lifetime problem for ultracompact HII regions.Comment: 12 pages, 3 figures, Accepted for publication in the Astrophysical Journal Letter

Broad Recombination Line Objects in W49N on 600 AU Scales

High resolution 7 mm observations of the W49N massive star forming region have detected recombination line emission from the individual ultracompact (UC) HII regions on 50 milliarcsecond (600 AU) scales. These line observations, combined with multifrequency, high-resolution continuum imaging of the region at 7 mm (VLA) and at 3 mm and 1 mm (BIMA), indicate that five to seven of the eighteen ultracompact sources in W49N are broad recombination line objects (BRLOs) as described by Jaffe & Martin-Pintado (1999). BRLOs have both broad radio recombination lines ($\Delta$V$>$60 \kms) and rising spectra (S$_{\nu}\sim\nu^{\alpha}$), with $\alpha$ values greater than 0.4. The broad line widths of the H52$\alpha$ line are probably related to motions in the ionized gas rather than pressure broadening. A number of models have been proposed to explain the long lifetime of UC HII regions, including the photoevaporated disk model proposed by Hollenbach et al. (1994). This model can also explain the broad lines, rising spectra and bipolar morphologies of some sources. We suggest$-$based on line and continuum observations as well as source morphology$-$that in a subset of the W49N ultracompact sources we may be observing ionized winds that arise from circumstellar disks.Comment: 15 pages, 2 figures, to appear in The Astrophysical Journal (v. 600, no. 1), 1 January 200