arXiv subjects

M. J. Claussen

Publications and source records attributed to M. J. Claussen.

At least 19 recordsLinked to original sources

arXiv2022

Ground Vibrational State SiO Emission in the VLA BAaDE Survey

Using a subsample of the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey of stellar SiO masers, we explore the prevalence and characteristics of $^{28}$SiO $J=1-0, v=0$ emission. We identify 90 detections of maser, thermal, or composite $^{28}$SiO $J=1-0, v=0$ emission out of approximately 13,000 candidate spectra from the NSF's Karl G. Jansky Very Large Array (VLA). We find that the detected sources are likely asymptotic giant branch (AGB) stars belonging to a bright, foreground Milky Way stellar disk population. For the 32 sources showing thermal components, we extract values for outflow velocity by fitting thermal line profiles. We find a range of circumstellar envelope expansion velocities, and compare to previously recorded OH and CO expansion velocities. This preliminary survey is already the largest study of stellar ground-vibrational-state SiO masers to date, and will be expanded to include the entire VLA BAaDE dataset when data reduction for the 18,988 target sources is completed.

astro-ph.GA↗

arXiv2018

Binarity and Accretion in AGB Stars: HST/STIS Observations of UV Flickering in Y Gem

Binarity is believed to dramatically affect the history and geometry of mass loss in AGB and post-AGB stars, but observational evidence of binarity is sorely lacking. As part of a project to search for hot binary companions to cool AGB stars using the GALEX archive, we discovered a late-M star, Y Gem, to be a source of strong and variable UV and X-ray emission. Here we report UV spectroscopic observations of Y Gem obtained with the Hubble Space Telescope that show strong flickering in the UV continuum on time-scales of <~20 s, characteristic of an active accretion disk. Several UV lines with P-Cygni-type profiles from species such as Si IV and C IV are also observed, with emission and absorption features that are red- and blue- shifted by velocities of ~500 km/s from the systemic velocity. Our model for these (and previous) observations is that material from the primary star is gravitationally captured by a companion, producing a hot accretion disk. The latter powers a fast outflow that produces blue-shifted features due to absorption of UV continuum emitted by the disk, whereas the red-shifted emission features arise in heated infalling material from the primary. The outflow velocities support a previous inference by Sahai et al. (2015) that Y Gem's companion is a low-mass main-sequence star. Blackbody fitting of the UV continuum implies an accretion luminosity of about 13 Lsun and thus a mass-accretion rate >5e-7 Msun/yr; we infer that Roche lobe overflow is the most likely binary accretion mode for Y Gem.

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arXiv2017

SiS in the circumstellar envelope of IRC +10126: maser and quasi-thermal emission

We present new Effelsberg-100 m, ATCA, and VLA observations of rotational SiS transitions in the circumstellar envelope (CSE) of IRC +10216. Thanks to the high angular resolution achieved by the ATCA observations, we unambiguously confirm that the molecule's J=1-0 transition exhibits maser action in this CSE, as first suggested more than thirty years ago. The maser emission's radial velocity peaking at a local standard of rest velocity of -39.862$\pm$0.065 km/s indicates that it arises from an almost fully accelerated shell. Monitoring observations show time variability of the SiS (1-0) maser. The two lowest-$J$ SiS quasi-thermal emission lines trace a much more extended emitting region than previous high-J SiS observations. Their distributions show that the SiS quasi-thermal emission consists of two components: one is very compact (radius<1.5", corresponding to <3$\times 10^{15}$ cm), and the other extends out to a radius >11". An incomplete shell-like structure is found in the north-east, which is indicative of existing SiS shells. Clumpy structures are also revealed in this CSE. The gain of the SiS (1-0) maser (optical depths of about -5 at the blue-shifted side and, assuming inversion throughout the entire line's velocity range, about -2 at the red-shifted side) suggests that it is unsaturated. The SiS (1-0) maser can be explained in terms of ro-vibrational excitation caused by infrared pumping, and we propose that infrared continuum emission is the main pumping source.

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arXiv2013

Detection of Class I Methanol (CH3OH) Maser Candidates in Supernova Remnants

We have used the Karl G. Jansky Very Large Array (VLA) to search for 36 GHz and 44 GHz methanol (CH3OH) lines in a sample of 21 Galactic supernova remnants (SNRs). Mainly the regions of the SNRs with 1720 MHz OH masers were observed. Despite the limited spatial extent covered in our search, methanol masers were detected in both G1.4-0.1 and W28. Additional masers were found in SgrAEast. More than 40 masers were found in G1.4-0.1 which we deduce are due to interactions between the SNR and at least two separate molecular clouds. The six masers in W28 are associated with the molecular cloud that is also associated with the OH maser excitation. We discuss the possibility that the methanol maser may be more numerous in SNRs than the OH maser, but harder to detect due to observational constraints.

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arXiv2013

Evidence of a Hadronic Origin for the TeV Source J1834-087

We report on the discovery of compact, narrow OH line emission from the hydroxl molecule at 1720 MHz toward the extended TeV source J1834-087. The origin of this high energy emission is unknown; it could be powered by one or more candidate neutron stars (leptonic) or by cosmic rays interacting with dense gas (hadronic). The OH emission is detected near the center of J1834-087, coincident with the radio continuum of the supernova remnant W41, and the radial velocity of the line is the same velocity as a giant molecular cloud along the line of sight. We argue that the OH is maser emission stimulated by the interaction of the W41 shock with the molecular cloud. The known correlation between gamma-ray bright supernova remnants and OH masers favors a hadronic interpretation for this high energy emission.

astro-ph.HE↗

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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arXiv2012

The size, luminosity and motion of the extreme carbon star IRC+10216 (CW Leonis)

Very Large Array observations of the extreme carbon star IRC+10216 at 7 mm wavelength with 40 milli-arcsecond resolution resolve the object's radio emission, which forms an almost round uniform disk of 83 milli arcseconds diameter, corresponding to 11 AU (for an assumed distance of 130 pc). We find a brightness temperature of 1630 K for the radio photosphere. Since the emission is optically thick, we can directly estimate IRC+10216's average luminosity, which is 8600 L(Sun). This value is in excellent agreement with what is predicted from the period-luminosity relation for carbon-rich Miras. Assuming an effective temperature of 2750 K for IRC+10216, it implies an optical photospheric diameter of 3.8 AU. Our precise determination of IRC+10216's proper motion fits the picture presented by far-ultraviolet and far-infrared wavelength observations of its interaction region with the interstellar medium (its "astrosphere"): the star moves roughly in the direction expected from the morphology of the termination shock and its astrotail structures. Calculation of its three dimensional velocity and an analysis of the kinematics of its surrounding interstellar medium (ISM) suggest an appreciable relative velocity of 42 km s/s, which is about half the value discussed in recent studies. This suggests a lower (time-averaged) mass loss rate and/or a higher ISM density than previously assumed.

astro-ph.SR↗

arXiv2012

Shocked and Scorched: The Tail of a Tadpole in an Interstellar Pond

We report multi-wavelength observations of the far-infrared source IRAS 20324+4057, including high-resolution optical imaging with HST, and ground-based near-infrared, millimeter-wave and radio observations. These data show an extended, limb-brightened, tadpole-shaped nebula with a bright, compact, cometary nebula located inside the tadpole head. Our molecular line observations indicate that the Tadpole is predominantly molecular, with a total gas mass exceeding 3.7 Msun. Our radio continuum imaging, and archival Spitzer IRAC images, show the presence of additional tadpole-shaped objects in the vicinity of IRAS 20324+4057 that share a common E-W head-tail orientation: we propose that these structures are small, dense molecular cores that originated in the Cygnus cloud and are now being (i) photoevaporated by the ultraviolet radiation field of the Cyg OB2 No. 8 cluster located to the North-West, and (ii) shaped by ram pressure of a distant wind source or sources located to the West, blowing ablated and photoevaporated material from their heads eastwards. The ripples in the tail of the Tadpole are interpreted in terms of instabilities at the interface between the ambient wind and the dense medium of the former.

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arXiv2011

An evla and carma study of dusty disks and torii with large grains in dying stars

We report the results of a pilot multiwavelength survey in the radio continuum (X, Ka and Q bands, i.e., from 3.6 cm to 7 mm) carried out with the EVLA in order to confirm the presence of very large dust grains in dusty disks and torii around the central stars in a small sample of post-AGB objects, as inferred from millimeter and sub-millimeter observations. Supporting mm-wave observations were also obtained with CARMA towards three of our sources. Our EVLA survey has resulted in a robust detection of our most prominent submm emission source, the pre-planetary nebula IRAS 22036+5306, in all three bands, and the disk-prominent post-AGB object, RV Tau, in one band. The observed fluxes are consistent with optically-thin free-free emission, and since they are insignificant compared to their submm/mm fluxes, we conclude that the latter must come from substantial masses of cool, large (mm-sized) grains. We find that the power-law emissivity in the cm-to-submm range for the large grains in IRAS22036 is nu^{beta}, with beta=1-1.3. Furthermore, the value of beta in the 3 to 0.85 mm range for the three disk-prominent post-AGB sources (beta < or = 0.4) is significantly lower than that of IRAS22036, suggesting that the grains in post-AGB objects with circumbinary disks are likely larger than those in the dusty waists of pre-planetary nebulae.

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arXiv2010

Proper Motions of H2O Masers in the Water Fountain Source IRAS 19190+1102

We report on the results of two epochs of Very Long Baseline Array (VLBA) observations of the 22 GHz water masers toward IRAS 19190+1102. The water maser emission from this object shows two main arc-shaped formations perpendicular to their NE-SW separation axis. The arcs are separated by ~280 mas in position, and are expanding outwards at an angular rate of 2.35 mas/yr. We detect maser emission at velocities between -53.3 km/s to +78.0 km/s and there is a distinct velocity pattern where the NE masers are blueshifted and the SW masers are redshifted. The outflow has a three-dimensional outflow velocity of 99.8 km/s and a dynamical age of about 59 yr. A group of blueshifted masers not located along the arcs shows a change in velocity of more than 35 km/s between epochs, and may be indicative of the formation of a new lobe. These observations show that IRAS 19190+1102 is a member of the class of "water fountain"' pre-planetary nebulae displaying bipolar structure

astro-ph.SR↗

arXiv2009

A Precise Distance to IRAS 00420+5530 via H2O Maser Parallax with the VLBA

We have used the VLBA to measure the annual parallax of the H2O masers in the star-forming region IRAS 00420+5530. This measurement yields a direct distance estimate of 2.17 +/- 0.05 kpc (<3%), which disagrees substantially with the standard kinematic distance estimate of ~4.6 kpc (according to the rotation curve of Brand and Blitz 1993), as well as most of the broad range of distances (1.7-7.7 kpc) used in various astrophysical analyses in the literature. The 3-dimensional space velocity of IRAS 00420+5530 at this new, more accurate distance implies a substantial non-circular and anomalously slow Galactic orbit, consistent with similar observations of W3(OH) (Xu et al., 2006; Hachisuka et al. 2006), as well as line-of-sight velocity residuals in the rotation curve analysis of Brand and Blitz (1993). The Perseus spiral arm of the Galaxy is thus more than a factor of two closer than previously presumed, and exhibits motions substantially at odds with axisymmetric models of the rotating Galaxy.

astro-ph.GA↗

arXiv2007

An Inner Hole in the Disk around TW Hydrae Resolved in 7 Millimeter Dust Emission

We present Very Large Array observations at 7 millimeters wavelength that resolve the dust emission structure in the disk around the young star TW Hydrae at the scale of the ~4 AU (~0.16") radius inner hole inferred from spectral energy distribution modeling. These high resolution data confirm directly the presence of an inner hole in the dust disk and reveal a high brightness ring that we associate with the directly illuminated inner edge of the disk. The clearing of the inner disk plausibly results from the dynamical effects of a giant planet in formation. In an appendix, we develop an analytical framework for the interpretation of visibility curves from power-law disk models with inner holes.

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arXiv2006

VLA+PT Astrometry of 46 Radio Stars

We have used the Very Large Array (VLA), linked with the Pie Town Very Long Baseline Array antenna, to determine astrometric positions of 46 radio stars in the International Celestial Reference Frame (ICRF). Positions were obtained in the ICRF directly through phase referencing of the stars to nearby ICRF quasars whose positions are accurate at the 0.25 mas level. Radio star positions are estimated to be accurate at the 10 mas level, with position errors approaching a few milli-arcseconds for some of the stars observed. Our measured positions were combined with previous measurements taken from as early as 1978 to obtain proper motion estimates for all 46 stars with average uncertainties of ~1.7 mas/yr. We compared our radio star positions and proper motions with the Hipparcos Catalogue data, and find consistency in the reference frames produced by each data set on the 1-sigma level, with errors of ~2.7 mas per axis for the reference frame orientation angles at our mean epoch of 2003.78. No significant spin is found between our radio data frame and the Hipparcos Celestial Reference Frame (HCRF) with largest rotation rates of +0.55 and -0.41 mas/yr around the x and z axes, respectively, with 1-sigma errors of 0.36 mas/yr. Thus, our results are consistent with a non-rotating Hipparcos frame with respect to the ICRF.

astro-ph↗

arXiv2006

Radio continuum monitoring of the extreme carbon star IRC+10216

We describe Very Large Array observations of the extreme carbon star IRC+10216 at 8.4, 14.9, and 22.5 GHz made over a two year period. We find possible variability correlated with the infrared phase and a cm- to sub-millimeter wavelength spectral index very close to 2. The variability, observed flux densities, and upper limit on the size are consistent with the emission arising from the stellar photosphere or a slightly larger radio photosphere.

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arXiv2005

Towards Planetesimals in the Disk around TW Hya: 3.5 centimeter Dust Emission

We present Very Large Array observations at 3.5 cm of the nearby young star TW Hya that show the emission is constant in time over weeks, months and years, and spatially resolved with peak brightness temperature ~10 K at ~0.25 (15 AU) resolution. These features are naturally explained if the emission mechanism at this wavelength is thermal emission from dust particles in the disk surrounding the star. To account quantitatively for the observations, we construct a self-consistent accretion disk model that incorporates a population of centimeter size particles that matches the long wavelength spectrum and spatial distribution. A substantial mass fraction of orbiting particles in the TW Hya disk must have agglomerated to centimeter size. These data provide the first clear indication that dust emission from protoplanetary disks may be observed at centimeter wavelengths, and that changes in the spectral slope of the dust emission may be detected, providing constraints on dust evolution and the planet formation process.

astro-ph↗

arXiv2005

The OH (1720 MHz) Supernova Remnant Masers in W44: MERLIN and VLBA Polarization Observations

Full-polarization MERLIN and VLBA observations of the 1720-MHz maser emission from the OH molecule in the supernova remnant W44 are presented. Zeeman splitting has been directly resolved between right- and left-circularly polarized spectra indicating magnetic field strengths of B~0.50 mG. The position angle of the linear polarization is in good agreement with the orientation of the shocked gas at the supernova remnant/molecular cloud interface. Based on MERLIN data having a resolution of 200 milliarcseconds (mas) and VLBA data with a resolution of 15 mas, the masers are measured to have deconvolved angular sizes of 50 to 350 mas (150 to 1000 AU) with compact cores 20 mas (60 AU) in size, consistent with theoretical expectation and previous observations.

astro-ph↗

arXiv2005

High resolution radio observations of the colliding-wind binary WR140

Milli-arcsecond resolution Very Long Baseline Array (VLBA) observations of the archetype WR+O star colliding-wind binary (CWB) system WR140 are presented for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in the wind-collision region (WCR) is clearly resolved as a bow-shaped arc that rotates as the orbit progresses. We interpret this rotation as due to the O star moving from SE to approximately E of the WR star, which leads to solutions for the orbit inclination of 122+/-5 deg, the longitude of the ascending node of 353+/-3 deg, and an orbit semi-major axis of 9.0+/-0.5 mas. The distance to WR140 is determined to be 1.85+/-0.16 kpc, which requires the O star to be a supergiant. The inclination implies the mass of the WR and O star to be 20+/-4 and 54+/-10 solar masses respectively. We determine a wind-momentum ratio of 0.22, with an expected half-opening angle for the WCR of 63 deg, consistent with 65+/-10 deg derived from the VLBA observations. Total flux measurements from Very Large Array (VLA) observations show the radio emission from WR140 is very closely the same from one orbit to the next, pointing strongly toward emission, absorption and cooling mechanism(s) that are controlled largely by the orbital motion. The synchrotron spectra evolve dramatically through the orbital phases observed, exhibiting both optically thin and optically thick emission. We discuss a number of absorption and cooling mechanisms that may determine the evolution of the synchrotron spectrum with orbital phase.

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arXiv2004

The OH (1720 MHz) Supernova Remnant Masers in W28: MERLIN and VLBA Polarization Observations

Full-polarization MERLIN and VLBA observations of the 1720 MHz maser emission from the OH molecule in the supernova remnant W28 are presented. Zeeman splitting (|B| \approx 0.75 mG) has been directly resolved between right- and left-circularly polarized spectra for the first time. Linear-polarization position angles and circular-polarization Zeeman splitting observed in the maser emission permit interpretation of a comprehensive picture of the magnetic field at the supernova/molecular cloud interface marked by the masers. We find the post-SNR-shock magnetic field to be well-ordered over the ~1 pc covered by the maser region (compared with the approximately 30-pc diameter of the entire SNR) and well-aligned with the shock front that is traced by synchrotron radiation and molecular emission. Based on MERLIN data having a resolution of 200 mas and VLBA data with a resolution of 15 mas, the masers are measured to have deconvolved angular sizes of 90 to 350 mas (225 to 875 AU) with compact cores 20 mas (50 AU) in size, consistent with theoretical expectation and previous observations.

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