arXiv subjects

C. L. Brogan

Publications and source records attributed to C. L. Brogan.

At least 55 records · Page 3Linked to original sources

arXiv2016

Planck intermediate results. XXXI. Microwave survey of Galactic supernova remnants

The all-sky Planck survey in 9 frequency bands was used to search for emission from all 274 known Galactic supernova remnants. Of these, 16 were detected in at least two Planck frequencies. The radio-through-microwave spectral energy distributions were compiled to determine the emission mechanism for microwave emission. In only one case, IC 443, is there high-frequency emission clearly from dust associated with the supernova remnant.In all cases, the low-frequency emission is from synchrotron radiation. A single power law, as predicted for a population of relativistic particles with energy distribution that extends continuously to high energies, is evident for many sources, including the Crab and PKS 1209-51/52. A decrease in flux density relative to the extrapolation of radio emission is evident in several sources. Their spectral energy distributions can be approximated as broken power laws, $S_ν\proptoν^{-α}$, with the spectral index, alpha, increasing by 0.5-1 above a break frequency in the range 10-60 GHz. The break could be due to synchrotron losses.

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arXiv2015

An Overview of the 2014 ALMA Long Baseline Campaign

A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ~15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from September to late November 2014, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ~350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

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arXiv2015

ALMA Observations of Asteroid 3 Juno at 60 Kilometer Resolution

We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum images of the asteroid 3 Juno obtained with an angular resolution of 0.042 arcseconds (60 km at 1.97 AU). The data were obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. A sequence of ten consecutive images reveals continuous changes in the asteroid's profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the Database of Asteroid Models from Inversion Techniques. We measure a geometric mean diameter of 259pm4 km, in good agreement with past estimates from a variety of techniques and wavelengths. Due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. The median peak brightness temperature is 215pm13 K, while the median over the whole surface is 197pm15 K. With the unprecedented resolution of ALMA, we find that the brightness temperature varies across the surface with higher values correlated to the subsolar point and afternoon areas, and lower values beyond the evening terminator. The dominance of the subsolar point is accentuated in the final four images, suggesting a reduction in the thermal inertia of the regolith at the corresponding longitudes, which are possibly correlated to the location of the putative large impact crater. These results demonstrate ALMA's potential to resolve thermal emission from the surface of main belt asteroids, and to measure accurately their position, geometric shape, rotational period, and soil characteristics.

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arXiv2015

First Results from High Angular Resolution ALMA Observations Toward the HL Tau Region

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0.075 arcseconds (10 AU) to 0.025 arcseconds (3.5 AU), revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72pm0.05 degrees) and position angle (+138.02pm0.07 degrees). We obtain a high-fidelity image of the 1.0 mm spectral index ($α$), which ranges from $α\sim2.0$ in the optically-thick central peak and two brightest rings, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation include an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO+ (1-0) which exhibits a pattern over LSR velocities from 2-12 km/s consistent with Keplerian motion around a ~1.3 solar mass star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protostars XZ Tau (A/B) and LkHa358 at 2.9 mm.

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arXiv2015

ALMA Long Baseline Observations of the Strongly Lensed Submillimeter Galaxy HATLAS J090311.6+003906 at z=3.042

We present initial results of very high resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the $z$=3.042 gravitationally lensed galaxy HATLAS J090311.6+003906 (SDP.81). These observations were carried out using a very extended configuration as part of Science Verification for the 2014 ALMA Long Baseline Campaign, with baselines of up to 15 km. We present continuum imaging at 151, 236 and 290 GHz, at unprecedented angular resolutions as fine as 23 milliarcseconds (mas), corresponding to an un-magnified spatial scale of ~180 pc at z=3.042. The ALMA images clearly show two main gravitational arc components of an Einstein ring, with emission tracing a radius of ~1.5". We also present imaging of CO(10-9), CO(8-7), CO(5-4) and H2O line emission. The CO emission, at an angular resolution of ~170 mas, is found to broadly trace the gravitational arc structures but with differing morphologies between the CO transitions and compared to the dust continuum. Our detection of H2O line emission, using only the shortest baselines, provides the most resolved detection to date of thermal H2O emission in an extragalactic source. The ALMA continuum and spectral line fluxes are consistent with previous Plateau de Bure Interferometer and Submillimeter Array observations despite the impressive increase in angular resolution. Finally, we detect weak unresolved continuum emission from a position that is spatially coincident with the center of the lens, with a spectral index that is consistent with emission from the core of the foreground lensing galaxy.

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arXiv2015

Subarcsecond Submillimeter Imaging of the Ultracompact HII Region G5.89-0.39

We present the first subarcsecond submillimeter images of the enigmatic ultracompact HII region (UCHII) G5.89-0.39. Observed with the SMA, the 875 micron continuum emission exhibits a shell-like morphology similar to longer wavelengths. By using images with comparable angular resolution at five frequencies obtained from the VLA archive and CARMA, we have removed the free-free component from the 875 micron image. We find five sources of dust emission: two compact warm objects (SMA1 and SMA2) along the periphery of the shell, and three additional regions further out. There is no dust emission inside the shell, supporting the picture of a dust-free cavity surrounded by high density gas. At subarcsecond resolution, most of the molecular gas tracers encircle the UCHII region and appear to constrain its expansion. We also find G5.89-0.39 to be almost completely lacking in organic molecular line emission. The dust cores SMA1 and SMA2 exhibit compact spatial peaks in optically-thin gas tracers (e.g. 34SO2), while SMA1 also coincides with 11.9 micron emission. In CO(3-2), we find a high-velocity north/south bipolar outflow centered on SMA1, aligned with infrared H2 knots, and responsible for much of the maser activity. We conclude that SMA1 is an embedded intermediate mass protostar with an estimated luminosity of 3000 Lsun and a circumstellar mass of ~1 Msun. Finally, we have discovered an NH3 (3,3) maser 12 arcsec northwest of the UCHII region, coincident with a 44 GHz CH3OH maser, and possibly associated with the Br gamma outflow source identified by Puga et al. (2006).

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arXiv2015

The Physical Conditions in a Pre Super Star Cluster Molecular Cloud in the Antennae Galaxies

We present an analysis of the physical conditions in an extreme molecular cloud in the Antennae merging galaxies. This cloud has properties consistant with those required to form a globular cluster. We have obtained ALMA CO and 870$μ$m observations of the Antennae galaxy system with $\sim 0".5$ resolution. This cloud stands out in the data with a radius of $\lesssim 24$~pc and mass of $>5\times 10^6$~M$_\odot$. The cloud appears capable of forming a globular cluster, but the lack of associated thermal radio emission indicates that star formation has not yet altered the environment. The lack of thermal radio emission places the cloud in an early stage of evolution, which we expect to be short-lived ($\lesssim 1$~Myr) and thus rare. Given its mass and kinetic energy, for the cloud to be confined (as its appearance strongly suggests) it must be subject to an external pressure of P/$k_B \gtrsim 10^8$~K~cm$^{-3}$ -- 10,000 times higher than typical interstellar pressure. This would support theories that high pressures are required to form globular clusters and may explain why extreme environments like the Antennae are preferred environments for generating such objects. Given the cloud temperature of $\sim 25$~K, the internal pressure must be dominated by non-thermal processes, most likely turbulence. We expect the molecular cloud to collapse and begin star formation in $\lesssim 1$~Myr.

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arXiv2014

G11.92-0.61-MM2: A Bonafide Massive Prestellar Core?

Core accretion models of massive star formation require the existence of stable massive starless cores, but robust observational examples of such objects have proven elusive. We report subarcsecond-resolution SMA 1.3 mm, 1.1 mm, and 0.88 mm and VLA 1.3 cm observations of an excellent massive starless core candidate, G11.92-0.61-MM2, initially identified in the course of studies of GLIMPSE Extended Green Objects (EGOs). Separated by ~7.2" from the nearby MM1 protostellar hot core, MM2 is a strong, compact dust continuum source (submillimeter spectral index alpha=2.6+/-0.1), but is devoid of star formation indicators. In contrast to MM1, MM2 has no masers, no centimeter continuum, and no (sub)millimeter wavelength line emission in ~24 GHz of bandwidth observed with the SMA, including N2H+(3-2), HCO+(3-2), and HCN(3-2). Additionally, there is no evidence for an outflow driven by MM2. The (sub)millimeter spectral energy distribution (SED) of MM2 is best fit with a dust temperature of ~17-19 K and luminosity of ~5-7 L_sun. The combined physical properties of MM2, as inferred from its dust continuum emission, are extreme: M>30 M_sun within a radius<1000 AU, N(H2)>10^25 cm^-2 and n(H2)>10^9 cm^-3. Comparison of the molecular abundance limits derived from our SMA observations with gas-grain chemical models indicates that extremely dense (n(H)>>10^8 cm^-3), cold (<20 K) conditions are required to explain the lack of observed (sub)millimeter line emission, consistent with the dust continuum results. Our data suggest that G11.92-0.61-MM2 is the best candidate for a bonafide massive prestellar core found to date, and a promising target for future, higher-sensitivity observations.

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arXiv2014

Subarcsecond Imaging of the NGC 6334 I(N) Protocluster: Two Dozen Compact Sources and a Massive Disk Candidate

Using the SMA and VLA, we have imaged the massive protocluster NGC6334I(N) at high angular resolution (0.5"~650AU) from 6cm to 0.87mm, detecting 18 new compact continuum sources. Three of the new sources are coincident with previously-identified water masers. Together with the previously-known sources, these data bring the number of likely protocluster members to 25 for a protostellar density of ~700 pc^-3. Our preliminary measurement of the Q-parameter of the minimum spanning tree is 0.82 -- close to the value for a uniform volume distribution. All of the (nine) sources with detections at multiple frequencies have SEDs consistent with dust emission, and two (SMA1b and SMA4) also have long wavelength emission consistent with a central hypercompact HII region. Thermal spectral line emission, including CH3CN, is detected in six sources: LTE model fitting of CH3CN(J=12-11) yields temperatures of 72-373K, confirming the presence of multiple hot cores. The fitted LSR velocities range from -3.3 to -7.0 km/s, with an unbiased mean square deviation of 2.05 km/s, implying a dynamical mass of 410+-260 Msun for the protocluster. From analysis of a wide range of hot core molecules, the kinematics of SMA1b are consistent with a rotating, infalling Keplerian disk of diameter 800AU and enclosed mass of 10-30 Msun that is perpendicular (within 1 degree) to the large-scale bipolar outflow axis. A companion to SMA1b at a projected separation of 0.45" (590AU; SMA1d), which shows no evidence of spectral line emission, is also confirmed. Finally, we detect one 218.440GHz and several 229.7588GHz Class-I methanol masers.

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arXiv2014

Chasing the Identification of ASCA Galactic Objects (ChIcAGO) - An X-ray Survey of Unidentified Sources in the Galactic Plane I: Source Sample and Initial Results

We present the Chasing the Identification of ASCA Galactic Objects (ChIcAGO) survey, which is designed to identify the unknown X-ray sources discovered during the ASCA Galactic Plane Survey (AGPS). Little is known about most of the AGPS sources, especially those that emit primarily in hard X-rays (2-10 keV) within the F_x ~ 10^-13 to 10^-11 erg cm^-2 s^-1 X-ray flux range. In ChIcAGO, the subarcsecond localization capabilities of Chandra have been combined with a detailed multi-wavelength follow-up program, with the ultimate goal of classifying the >100 unidentified sources in the AGPS. Overall to date, 93 unidentified AGPS sources have been observed with Chandra as part of the ChIcAGO survey. A total of 253 X-ray point sources have been detected in these Chandra observations within 3' of the original ASCA positions. We have identified infrared and optical counterparts to the majority of these sources, using both new observations and catalogs from existing Galactic plane surveys. X-ray and infrared population statistics for the X-ray point sources detected in the Chandra observations reveal that the primary populations of Galactic plane X-ray sources that emit in the F_x ~ 10^-13 to 10^-11 erg cm^-2 s^-1 flux range are active stellar coronae, massive stars with strong stellar winds that are possibly in colliding-wind binaries, X-ray binaries, and magnetars. There is also a fifth population that is still unidentified but, based on its X-ray and infrared properties, likely comprise partly of Galactic sources and partly of active galactic nuclei.

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arXiv2013

OH (1720 MHz) Masers: A Multiwavelength Study of the Interaction between the W51C Supernova Remnant and the W51B Star Forming Region

We present a comprehensive view of the W51B HII region complex and the W51C supernova remnant (SNR) using new radio observations from the VLA, VLBA, MERLIN, JCMT, and CSO along with archival data from Spitzer, ROSAT, ASCA, and Chandra. Our VLA data include the first 400 cm (74 MHz) continuum image of W51 at high resolution (88 arcsec). The 400 cm image shows non-thermal emission surrounding the G49.2-0.3 HII region, and a compact source of non-thermal emission (W51B_NT) coincident with the previously-identified OH (1720 MHz) maser spots, non-thermal 21 and 90 cm emission, and a hard X-ray source. W51B_NT falls within the region of high likelihood for the position of TeV gamma-ray emission. Using the VLBA three OH (1720 MHz) maser spots are detected in the vicinity of W51B_NT with sizes of 60 to 300 AU and Zeeman effect magnetic field strengths of 1.5 to 2.2 mG. The multiwavelength data demonstrate that the northern end of the W51B HII region complex has been partly enveloped by the advancing W51C SNR and this interaction explains the presence of W51B_NT and the OH masers. This interaction also appears in the thermal molecular gas which partially encircles W51B_NT and exhibits narrow pre-shock (DeltaV 5 km/s) and broad post-shock (DeltaV 20 km/s) velocity components. RADEX radiative transfer modeling of these two components yield physical conditions consistent with the passage of a non-dissociative C-type shock. Confirmation of the W51B/W51C interaction provides additional evidence in favor of this region being one of the best candidates for hadronic particle acceleration known thus far.

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arXiv2013

VLA OH Zeeman Observations of the star forming region S88B

We present observations of the Zeeman effect in OH thermal absorption main lines at 1665 and 1667 MHz taken with the Very Large Array (VLA) toward the star forming region S88B. The OH absorption profiles toward this source are complicated, and contain several blended components toward a number of positions. Almost all of the OH absorbing gas is located in the eastern parts of S88B, toward the compact continuum source S88B-2 and the eastern parts of the extended continuum source S88B-1. The ratio of 1665/1667 MHz OH line intensities indicates the gas is likely highly clumped, in agreement with other molecular emission line observations in the literature. S88-B appears to present a similar geometry to the well-known star forming region M17, in that there is an edge-on eastward progression from ionized to molecular gas. The detected magnetic fields appear to mirror this eastward transition; we detected line-of-sight magnetic fields ranging from 90-400 μG, with the lowest values of the field to the southwest of the S88B-1 continuum peak, and the highest values to its northeast. We used the detected fields to assess the importance of the magnetic field in S88B by a number of methods; we calculated the ratio of thermal to magnetic pressures, we calculated the critical field necessary to completely support the cloud against self-gravity and compared it to the observed field, and we calculated the ratio of mass to magnetic flux in terms of the critical value of this parameter. All these methods indicated that the magnetic field in S88B is dynamically significant, and should provide an important source of support against gravity. Moreover, the magnetic energy density is in approximate equipartition with the turbulent energy density, again pointing to the importance of the magnetic field in this region.

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arXiv2012

The Protocluster G18.67+0.03: A Test Case for Class I Methanol Masers as Evolutionary Indicators for Massive Star Formation

We present high angular resolution Submillimeter Array (SMA) and Karl G. Jansky Very Large Array (VLA) observations of the massive protocluster G18.67+0.03. Previously targeted in maser surveys of GLIMPSE Extended Green Objects (EGOs), this cluster contains three Class I methanol maser sources, providing a unique opportunity to test the proposed role of Class I masers as evolutionary indicators for massive star formation. The millimeter observations reveal bipolar molecular outflows, traced by 13CO(2-1) emission, associated with all three Class I maser sources. Two of these sources (including the EGO) are also associated with 6.7 GHz Class II methanol masers; the Class II masers are coincident with millimeter continuum cores that exhibit hot core line emission and drive active outflows, as indicated by the detection of SiO(5-4). In these cases, the Class I masers are coincident with outflow lobes, and appear as clear cases of excitation by active outflows. In contrast, the third Class I source is associated with an ultracompact HII region, and not with Class II masers. The lack of SiO emission suggests the 13CO outflow is a relic, consistent with its longer dynamical timescale. Our data show that massive young stellar objects associated only with Class I masers are not necessarily young, and provide the first unambiguous evidence that Class I masers may be excited by both young (hot core) and older (UC HII) MYSOs within the same protocluster.

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arXiv2012

Molecular line survey of the high-mass star-forming region NGC 6334I with Herschel/HIFI and the SMA

We aim at deriving the molecular abundances and temperatures of the hot molecular cores in the high-mass star-forming region NGC 6334I and consequently deriving their physical and astrochemical conditions. In the framework of the Herschel guaranteed time key program CHESS, NGC 6334I is investigated by using HIFI aboard the Herschel Space Observatory. A spectral line survey is carried out in the frequency range 480-1907 GHz, and auxiliary interferometric data from the SMA in the 230 GHz band provide spatial information for disentangling the different physical components contributing to the HIFI spectrum. The spectral lines are identified with the aid of former surveys and spectral line catalogs. The observed spectrum is then compared to a simulated synthetic spectrum with XCLASS, assuming local thermal equilibrium, and best fit parameters are derived using the model optimization package MAGIX. A total of 46 molecules are identified, with 31 isotopologues, resulting in about 4300 emission and absorption lines. High- energy levels of the dominant emitter methanol and vibrationally excited HCN are detected. The number of unidentified lines remains low with 75, or less than 2 percent of the lines detected. The modeling suggests that several spectral features need two or more components to be fitted properly. Other components could be assigned to cold foreground clouds or to outflows, most visible in the SiO emission. A chemical variation between the two embedded hot cores is found, with more N-bearing molecules identified in SMA1 and O-bearing molecules in SMA2. Spectral line surveys give powerful insights into the study of the interstellar medium. Different molecules trace different physical conditions like the inner hot core, the envelope, the outflows or the cold foreground clouds. The derived molecular abundances provide further constraints for astrochemical models.

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arXiv2011

Deep Very Large Array Radio Continuum Surveys of GLIMPSE Extended Green Objects (EGOs)

We present the results of deep, high angular resolution Very Large Array (VLA) surveys for radio continuum emission towards a sample of 14 GLIMPSE Extended Green Objects (EGOs). Identified as massive young stellar object (MYSO) outflow candidates based on their extended 4.5 micron emission in Spitzer images, the EGOs in our survey sample are also associated with 6.7 GHz Class II and/or 44 GHz Class I methanol masers. No continuum is detected at 3.6 or 1.3 cm towards the majority (57%) of our targets (median rms ~0.03 and 0.25 mJy/beam). Only two EGOs are associated with optically thin emission consistent with ultracompact/compact HII regions. Both of these sources exhibit cm-wavelength multiplicity, with evidence that one of the less-evolved members may be driving the 4.5 micron outflow. Most of the other cm-wavelength EGO counterparts are weak (< 1 mJy), unresolved, undetected at 1.3 cm, and characterized by intermediate spectral indices consistent with hypercompact (HC) HII regions or ionized winds or jets. One EGO cm counterpart, likely an optically thick HC HII region, is detected only at 1.3 cm and is associated with hot core line emission and water and 6.7 GHz methanol masers. The results of our exceptionally sensitive survey indicate that EGOs signify an early stage of massive star formation, before photoionizing feedback from the central MYSO significantly influences the (proto)cluster environment. Actively driving outflows (and so, presumably, actively accreting), the surveyed EGOs are associated with significant clump-scale gas reservoirs, providing sufficient material for sustained, rapid accretion.

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arXiv2011

First Results from a 1.3 cm EVLA Survey of Massive Protostellar Objects: G35.03+0.35

We have performed a 1.3 centimeter survey of 24 massive young stellar objects (MYSOs) using the Expanded Very Large Array (EVLA). The sources in the sample exhibit a broad range of massive star formation signposts including Infrared Dark Clouds (IRDCs), UCHII regions, and extended 4.5 micron emission in the form of Extended Green Objects (EGOs). In this work, we present results for G35.03+0.35 which exhibits all of these phenomena. We simultaneously image the 1.3 cm ammonia (1,1) through (6,6) inversion lines, four methanol transitions, two H recombination lines, plus continuum at 0.05 pc resolution. We find three areas of thermal ammonia emission, two within the EGO (designated the NE and SW cores) and one toward an adjacent IRDC. The NE core contains an UCHII region (CM1) and a candidate HCHII region (CM2). A region of non-thermal, likely masing ammonia (3,3) and (6,6) emission is coincident with an arc of 44 GHz methanol masers. We also detect two new 25 GHz Class I methanol masers. A complementary Submillimeter Array 1.3 mm continuum image shows that the distribution of dust emission is similar to the lower-lying ammonia lines, all peaking to the NW of CM2, indicating the likely presence of an additional MYSO in this protocluster. By modeling the ammonia and 1.3 mm continuum data, we obtain gas temperatures of 20-220 K and masses of 20-130 solar. The diversity of continuum emission properties and gas temperatures suggest that objects in a range of evolutionary states exist concurrently in this protocluster.

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arXiv2010

Bipolar Molecular Outflows and Hot Cores in GLIMPSE Extended Green Objects (EGOs)

We present high angular resolution Submillimeter Array (SMA) and Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations of two GLIMPSE Extended Green Objects (EGOs)--massive young stellar object (MYSO) outflow candidates identified based on their extended 4.5 micron emission in Spitzer images. The mm observations reveal bipolar molecular outflows, traced by high-velocity 12CO(2-1) and HCO+(1-0) emission, coincident with the 4.5 micron lobes in both sources. SiO(2-1) emission confirms that the extended 4.5 micron emission traces active outflows. A single dominant outflow is identified in each EGO, with tentative evidence for multiple flows in one source (G11.92-0.61). The outflow driving sources are compact millimeter continuum cores, which exhibit hot-core spectral line emission and are associated with 6.7 GHz Class II methanol masers. G11.92-0.61 is associated with at least three compact cores: the outflow driving source, and two cores that are largely devoid of line emission. In contrast, G19.01-0.03 appears as a single MYSO. The difference in multiplicity, the comparative weakness of its hot core emission, and the dominance of its extended envelope of molecular gas all suggest that G19.01-0.03 may be in an earlier evolutionary stage than G11.92-0.61. Modeling of the G19.01-0.03 spectral energy distribution suggests that a central (proto)star (M ~10 Msun) has formed in the compact mm core (Mgas ~ 12-16 Msun), and that accretion is ongoing at a rate of ~10^-3 solar masses per year. Our observations confirm that these EGOs are young MYSOs driving massive bipolar molecular outflows, and demonstrate that considerable chemical and evolutionary diversity are present within the EGO sample.

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arXiv2010

Identification of a Population of X-ray Emitting Massive Stars in the Galactic Plane

We present X-ray, infrared, optical and radio observations of four previously unidentified Galactic plane X-ray sources, AX J163252-4746, AX J184738-0156, AX J144701-5919 and AX J144547-5931. Detection of each source with the Chandra X-ray Observatory has provided sub-arcsecond localizations, which we use to identify bright infrared counterparts to all four objects. Infrared and optical spectroscopy of these counterparts demonstrate that all four X-ray sources are extremely massive stars, with spectral classifications Ofpe/WN9 (AX J163252-4746), WN7 (AX J184738-0156 = WR121a), WN7-8h (AX J144701-5919) and OIf+ (AX J144547-5931). AX J163252-4746 and AX J184738-0156 are both luminous, hard, X-ray emitters with strong Fe XXV emission lines in their X-ray spectra at ~6.7 keV. The multi-wavelength properties of AX J163252-4746 and AX J184738-0156 are not consistent with isolated massive stars or accretion onto a compact companion; we conclude that their X-ray emission is most likely generated in a colliding-wind binary system. For both AX J144701-5919 and AX J144547-5931, the X-ray emission is an order of magnitude less luminous and with a softer spectrum. These properties are consistent with a colliding-wind binary interpretation for these two sources also, but other mechanisms for the generation of X-rays cannot be excluded. There are many other as yet unidentified X-ray sources in the Galactic plane, with X-ray properties similar to those seen for AX J163252-4746, AX J184738-0156, AX J144701-5919 and AX J144547-5931. This may indicate a substantial population of X-ray-emitting massive stars and colliding-wind binaries in the Milky Way.

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