Trigonometric Parallaxes of Massive Star Forming Regions: II. Cep A & NGC 7538

We report trigonometric parallaxes for the sources NGC 7538 and Cep A, corresponding to distances of 2.65 [+0.12/-0.11] kpc and 0.70 [+0.04/-0.04] kpc, respectively. The distance to NGC 7538 is considerably smaller than its kinematic distance and places it in the Perseus spiral arm. The distance to Cep A is also smaller than its kinematic distance and places it in the Local arm or spur. Combining the distance and proper motions with observed radial velocities gives the location and full space motion of the star forming regions. We find significant deviations from circular Galactic orbits for these sources: both sources show large peculiar motions (> 10 km/s) counter to Galactic rotation and NGC 7538 has a comparable peculiar motion toward the Galactic center.Comment: 21 pages, 8 figures; to appear in the Astrophysical Journa

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&

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 Bolocam Galactic Plane Survey. XIV. Physical Properties of Massive Starless and Star Forming Clumps

We sort $4683$ molecular clouds between $10^\circ< \ell <65^\circ$ from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact $70$ $\mu{\rm m}$ sources, mid-IR color-selected YSOs, ${\rm H_2O}$ and ${\rm CH_3OH}$ masers, and UCHII regions. We also present a combined ${\rm NH_3}$-derived gas kinetic temperature and ${\rm H_2O}$ maser catalog for $1788$ clumps from our own GBT 100m observations and from the literature. We identify a subsample of $2223$ ($47.5\%$) starless clump candidates, the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong ($>1$ dex) progressions when sorted by star formation indicator. The median starless clump candidate is marginally sub-virial ($\alpha \sim 0.7$) with $>75\%$ of clumps with known distance being gravitationally bound ($\alpha < 2$). These samples show a statistically significant increase in the median clump mass of $\Delta M \sim 170-370$ M$_\odot$ from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at $\dot{M}\sim200-440$ Msun Myr$^{-1}$ for an average free-fall $0.8$ Myr time-scale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, (iii) and/or a variation in the ratio of starless to protostellar clump lifetime that scales as $\sim M^{-0.4}$. By comparing to the observed number of ${\rm CH_3OH}$ maser containing clumps we estimate the phase-lifetime of massive ($M>10^3$ M$_\odot$) starless clumps to be $0.37 \pm 0.08 \ {\rm Myr} \ (M/10^3 \ {\rm M}_\odot)^{-1}$; the majority ($M<450$ M$_\odot$) have phase-lifetimes longer than their average free-fall time.Comment: Accepted for publication in ApJ; 33 pages; 22 figures; 7 table

Trigonometric Parallaxes of 6.7 GHz Methanol Masers

Emission from the 6.7 GHz methanol maser transition is very strong, is relatively stable, has small internal motions, and is observed toward numerous massive star-forming regions in the Galaxy. Our goal is to perform high-precision astrometry using this maser transition to obtain accurate distances to their host regions. Eight strong masers were observed during five epochs of VLBI observations with the European VLBI Network between 2006 June, and 2008 March. We report trigonometric parallaxes for five star-forming regions, with accuracies as good as $\sim22 \mathrm{\mu}$as. Distances to these sources are $2.57^{+0.34}_{-0.27}$ kpc for ON 1, $0.776^{+0.104}_{-0.083}$ kpc for L 1206, $0.929^{+0.034}_{-0.033}$ kpc for L 1287, $2.38^{+0.13}_{-0.12}$ kpc for NGC 281-W, and $1.59^{+0.07}_{-0.06}$ kpc for S 255. The distances and proper motions yield the full space motions of the star-forming regions hosting the masers, and we find that these regions lag circular rotation on average by $\sim$17 km s$^{-1}$, a value comparable to those found recently by similar studies.Comment: 17 pages, 21 figures, 5 tables, accepted for publication in A&A, corrected typo

Trastuzumab beyond progression: a cost-utility analysis

Background: The continuation of trastuzumab beyond progression in combination with capecitabine as secondary chemotherapy for HER2-positive metastatic breast cancer (MBC) prolongs progression-free survival without a substantial increase in toxicity. Patients and methods: A Markov cohort simulation was used to follow the clinical course of typical patients with MBC. Information on response rates and major adverse effects was derived, and transition probabilities were estimated, based on the results of the Breast International Group 03-05 clinical trial. Direct costs were assessed from the perspective of the Swiss health care system. Results: The addition of trastuzumab to capecitabine is estimated to cost on average an additional of €33 980 and to yield a gain of 0.35 quality-adjusted life years (QALYs), resulting in an incremental cost-effectiveness ratio of €98 329/QALYs gained. Probabilistic sensitivity analysis showed that the willingness-to-pay threshold of €60 000/QALY was reached in 12% of cases. Conclusion: The addition of trastuzumab to capecitabine in MBC patients is more expensive than what is typically regarded as cost-effective but falls within the value ranges found for established regimens in the treatment of MB

Near-infrared spectroscopy in NGC 7538

The characterisation of the stellar population toward young high-mass star-forming regions allows to constrain fundamental cluster properties like distance and age. These are essential when using high-mass clusters as probes to conduct Galactic studies. NGC 7538 is a star-forming region with an embedded stellar population only unearthed in the near-infrared. We present the first near-infrared spectro-photometric study of the candidate high-mass stellar content in NGC 7538. We obtained H and K spectra of 21 sources with both the multi-object and long-slit modes of LIRIS at the WHT, and complement these data with sub-arcsecond JHKs photometry of the region using the imaging mode of the same instrument. We find a wide variety of objects within the studied stellar population of NGC 7538. Our results discriminate between a stellar population associated to the HII region, but not contained within its extent, and several pockets of more recent star formation. We report the detection of CO bandhead emission toward several sources as well as other features indicative of a young stellar nature. We infer a spectro-photometric distance of 2.7+-0.5 kpc, an age spread in the range 0.5-2.2 Myr and a total mass ~1.7x10^3 Msun for the older population.Comment: 11 pages, 8 figures, 1 table, accepted by 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