Engineering topics

Mutel, R. L.

Publications and source records attributed to Mutel, R. L..

18 records

DOE OSTI2018

K2 Observations of SN 2018oh Reveal a Two-component Rising Light Curve for a Type Ia Supernova

We present an exquisite 30 minute cadence Kepler (K2) light curve of the Type Ia supernova (SN Ia) 2018oh (ASASSN-18bt), starting weeks before explosion, covering the moment of explosion and the subsequent rise, and continuing past peak brightness. These data are supplemented by multi-color Panoramic Survey Telescope (Pan-STARRS1) and Rapid Response System 1 and Cerro Tololo Inter-American Observatory 4 m Dark Energy Camera (CTIO 4-m DECam) observations obtained within hours of explosion. The K2 light curve has an unusual two-component shape, where the flux rises with a steep linear gradient for the first few days, followed by a quadratic rise as seen for typical supernovae (SNe) Ia. This "flux excess" relative to canonical SN Ia behavior is confirmed in our i-band light curve, and furthermore, SN 2018oh is especially blue during the early epochs. The flux excess peaks 2.14 ± 0.04 days after explosion, has a FWHM of 3.12 ± 0.04 days, a blackbody temperature of $T = 17,500^{+11,500}_{-9,000}$ K, a peak luminosity of 4.3 ± 0.2 x 10 38 erg s -1 , and a total integrated energy of 1.27 ± 0.01 x 10 43 erg. We compare SN 2018oh to several models that may provide additional heating at early times, including collision with a companion and a shallow concentration of radioactive nickel. While all of these models generally reproduce the early K2 light curve shape, we slightly favor a companion interaction, at a distance of ~ 2 x 10 12 based on our early color measurements, although the exact distance depends on the uncertain viewing angle. Additional confirmation of a companion interaction in future modeling and observations of SN 2018oh would provide strong support for a single-degenerate progenitor system.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

RADIO ASTROMETRY OF THE CLOSE ACTIVE BINARY HR 5110

The close active binary HR 5110 was observed at six epochs over 26 days using a global very long baseline interferometry array at 15.4 GHz. We used phase referencing to determine the position of the radio centroid at each epoch with an uncertainty significantly smaller than the component separation. After correcting for proper motion and parallax, we find that the centroid locations of all six epochs have barycenter separations consistent with an emission source located on the KIV secondary, and not in an interaction region between the stars or on the F primary. We used a homogeneous power-law gyrosynchrotron emission model to reproduce the observed flux densities and fractional circular polarization. The resulting ranges of mean magnetic field strength and relativistic electron densities are of the order of 10 G and 10{sup 5} cm{sup −3}, respectively, in the source region.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Wideband dynamic radio spectra of two ultra-cool dwarfs

A number of radio-loud ultra-cool dwarf (UCD) stars exhibit both continuous broadband and highly polarized pulsed radio emission. In order to determine the nature of the emission and the physical characteristics in the source region, we have made multi-epoch, wideband spectral observations of TVLM 0513-46 and 2M 0746+20. We combine these observations with archival radio data to fully characterize both the temporal and spectral properties of the radio emission. The continuum spectral energy distribution can be well modeled using gyrosynchrotron emission from mildly relativistic electrons in a dipolar field. The pulsed emission exhibits a variety of time-variable characteristics, including frequency drifts, frequency cutoffs, and multiple pulses per period. For 2M 0746+20 we determine a pulse period consistent with previously determined values. We modeled locations of pulsed emission using an oblique rotating magnetospheric model with beamed electron-cyclotron maser (ECM) sources. The best-fit models have narrow ECM beaming angles aligned with the local source magnetic field direction, except for one isolated burst from 2M 0746+20. For TVLM 0513-46, the best-fit rotation axis inclination is nearly orthogonal to the line of sight. For 2M 0746+20 we found a good fit using a fixed inclination i=36{sup ∘}, determined from optical observations. For both stars the ECM sources are located near feet of magnetic loops with radial extents 1.2R{sub s}–2.7R{sub s} and surface fields 2.2–2.5 kG. These results support recent suggestions that radio over-luminous UCDs have a global “weak field” non-axisymmetric magnetic topologies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

VERY LARGE ARRAY OBSERVATIONS OF DG TAU'S RADIO JET: A HIGHLY COLLIMATED THERMAL OUTFLOW

The active young protostar DG Tau has an extended jet that has been well studied at radio, optical, and X-ray wavelengths. We report sensitive new Very Large Array (VLA) full-polarization observations of the core and jet between 5 GHz and 8 GHz. Our high angular resolution observation at 8 GHz clearly shows an unpolarized inner jet with a size of 42 AU (0.''35) extending along a position angle similar to the optical-X ray outer jet. Using our nearly coeval 2012 VLA observations, we find a spectral index {alpha} = +0.46 {+-} 0.05, which combined with the lack of polarization is consistent with bremsstrahlung (free-free) emission, with no evidence for a non-thermal coronal component. By identifying the end of the radio jet as the optical depth unity surface, and calculating the resulting emission measure, we find that our radio results are in agreement with previous optical line studies of electron density and consequent mass-loss rate. We also detect a weak radio knot at 5 GHz located 7'' from the base of the jet, coincident with the inner radio knot detected by Rodriguez et al. in 2009 but at lower surface brightness. We interpret this as due to expansion of post-shock ionized gas in the three years between observations.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1995

Interstellar scattering toward Cygnus X-3: Measurements of anisotropy and of the inner scale

We present 18 cm wavelength Very Long Base Interferometry (VLBI) observations of Cyg X-3 obtained 1989 June 6 along with 18 and 20 cm Very Large Array (VLA) A-array data obtained 1985 February 8. In both data sets, the flux density was relatively high, and the intrinsic source size small compared to the scattering, ideal conditions for a detailed study of interstellar scattering. We find that the scattering disk is anisotropic, with an axial ratio 1.31 +/- 0.02 along position angle 52.0 deg +/- 1.5 deg. This is the first unambiguous measurement of anisotropic scattering in the interstellar medium. We also find a significant break in the phase structure function, the first measurement of a break in any source. The data exclude a steep turbulent spectrum, but are consistent with a shallow turbulent spectrum with an inner scale of 300 km, with a net uncertainty of approximately 50%. We tentatively identify the scattering plasma with the H II region DR 11, for which we estimate a visual extinction of 4 mag, and an emission measure toward Cyg X-3 of 6000 cm(exp -6)pc. We make the case that DR 11 is part of a shell of H II regions centered on the Cyg OB2 association (which is approximately 1.8 kpc distant) that is 2 deg (60 pc) in radius and expanding at 10 km/s. Our inner scale is consistent with that expected for an H II region, and the amount of scattering is consistent with the emission measure. We discuss how the anisotropy can be used to confirm the identification with DR 11 and to distinguish between different models of turbulence by comparison with measurements of the polarization of starlight along the line of sight.

Molnar, L. A.↗

NASA NTRS1988

Radio emission from RS CVn binaries. III - A VLA survey of 103 systems

The paper presents a 5 GHz radio survey of 103 close late-type stellar binaries. Fifty-three of the 103 candidate stars were detected above an average detection threshold of 0.4 mJy. The median observed radio luminosity is compared with total bolometric luminosity, rotational period, color index (B-V), and Rossby number.

Morris, D. H.↗

NASA NTRS1988

VLBI positions of eight stellar systems

Radio positions of eight stellar systems have been derived with accuracies of 3 to 300 milliarcseconds from MkIII VLBI observations conducted with multistation arrays. The best accuracy was obtained during a relatively strong outburst of the RS CVn system HR 5110. The epoch J2000.0 positions are obtained in the Jet Propulsion Laboratory VLBI reference frame of extragalactic radio sources.

Neill, A. E.↗

NASA NTRS1988

VLBI angular broadening measurements in the Cygnus region

Multiple-frequency VLBI observations of eight compact radio sources with lines of sight which cross the Galactic plane in Cyg are reported. The data are presented in a table and map and analyzed, with a focus on angular broadening (AB) induced by interstellar scattering. AB is confirmed in four of the sources, whereas the structures of the other four appear to be intrinsic. The AB is found to be limited to a region within a few deg of the Galactic plane.

Fey, A. L.↗

NASA NTRS1987

Radio emission from RS CVn binaries. II - Polarization and spectral properties

Multiepoch radio observations of circular polarization and spectral characteristics of several close, late-type stellar binaries are reported. The median luminosity of four well-studied systems ranged from 16.2 to 17.1 ergs/s/Hz. For individual systems, the fractional circular polarization decreases with increasing luminosity, particularly at frequencies above 5 GHz. Eclipsing binaries have significantly lower average circular polarization compared with noneclipsing systems. Helicity reversal is almost always observed between 1.4 and 4.9 GHz for systems with high orbital inclination. Comparison with ten years of previously published polarization observations for two RS CVn stellar systems show that the same helicity occurs at a given frequency for a given source, indicating a very stable, large-scale magnetic field geometry. These spectral and polarization characteristics strongly support a model of inhomogeneous gyrosynchrotron emission arising from electrons with power law energy spectra interacting with inhomogeneous magnetic fields.

Mutel, R. L.↗

NASA NTRS1986

Interstellar scattering of compact radio sources near supernova remnants

A multifrequency VLBI search for interstellar scattering of extragalactic radio sources near supernova remnants is reported. VLBI observations at 610, 1663, and 4991 MHz were made of compact sources near the supernova remnants CTA 1, G33.6 + 0.1, G74.9 + 1.2, and HB 21, and 610 MHz observations were also made of a source near HB 9. These observations were motivated by the possibility of enhanced cosmic ray-induced turbulence in front of supernova remnants, as expected in 'diffusive' theories of shock wave acceleration. Angular broadening is definitely seen in the case of the source 2013 + 370, which lies within 4 arcmin of the supernova remnant G74.9 + 1.2. Present observations cannot unambiguously attribute the scattering material to the supernova remnant, as the line of sight also passes through the Cygnus OB1 association. The source 1849 + 005 appears to be highly scattered, as fringes were not detected even on short baselines at 5 GHz. This result may be due to the low galactic longitude of this source rather than its proximity to the supernova remnant G 33.6 + 0.1. Broadening was not detected for sources whose lines of sight pass close to the supernova remnants HB 9, HB 21, and CTA 1.

Spangler, S. R.↗

NASA NTRS1985

Milliarcsecond structures, VLBI and optical positions of 8 HIPPARCOS radio stars

Mark 3 VLBI observations show evidence for complex radio structures on the milliarcsecond angular scale of 8 HIPPARCOS radio stars. Their VLBI positions and optical positions measured with the automatic meridian circle in Bordeaux are presented. Comparison between the optical and VLBI positions of these stars shows that the JPL VLBI reference frame and the FK4 fundamental catalog are aligned at the level of precision of the optical measurements (O".05).

Lestrade, J. F.↗

NASA NTRS1985

Radio emission from RS CVn binaries. I - VLA survey and period-radio luminosity relationship

A VLA survey of radio emission from 36 close binary stellar systems with RS CVn properties is reported. Eight new sources were detected. A summary of all published reports of radio emission from RS CVn systems is presented. There appears to be a correlation between maximum radio luminosity and rotational period, with a tentative functional form L(R) varies as P to the (-0.7) power. Rapid rotators (periods approximately 2 days) may be underluminous compared with the extrapolated trend from longer-period systems. The luminosity-period correlation probably results from a dynamo mechanism which produces strong magnetic fields and, in turn, enhances the nonthermal radio emission. The decrease in radio luminosity at short periods may be caused by a saturation of energy deposition in the chromosphere, possibly because the surface of the active star has become covered with spotted regions.

Mutel, R. L.↗

NASA NTRS1985

Dual polarization VLBI observations of stellar binary systems at 5 GHz

The binary systems Sigma CrB, SZ Psc, HR 1099, UX Ari, HR 5110, Algol, and Cyg X-1 are characterized in terms of marcsec-scale radio structure on the basis of dual-polarization observations at 4.969-4.997 GHz, obtained with an international VLBI array comprising the 100-m Effelsberg, 36-m Haystack, 42-m Green Bank, 26-m Fort Davis, 130-m-equivalent VLA, and 40-m Owens Valley telescopes (system temperatures 40-70 K) at 22-14 h UT on July 26-27, 1983. The data are presented in graphs and tables and discussed in detail. Single Gaussian brightness distributions with theta(FWHM) = 0.5-2.0 marcsec and brightness temperatures (2-200) x 10 to the 8th K are determined for four sources; core-halo structures are found for UX Ari and Algol; and an upper limit of 50 microarcsec is established for the angular separation of the regions of left and right circular polarization. The gross features seen in RS CVn systems are explained in terms of a simple expanding-coronal-loop model of flare events.

Mutel, R. L.↗

NASA NTRS1985

Radio polarization characteristics of two RS CVn binaries

The results of multifrequency epoch VLA observations of polarized radio emission from the nearby active RS CVn binaries UX Arietis and HR 1099 are reported. For both systems, there is an excellent correlation between handedness of circular polarization and frequency. Helicity reversal is almost always seen between 1.4 and 5.0 GHz, possibly due to optical depth effects. There may also be an anticorrelation between total intensity and fractional circular polarization, especially at 5 GHz. This is consistent with models in which intense flares are associated with compact selfabsorbed synchrotron sources, while the quiescent emission arises from larger gyrosynchrotron-emitting plasma.

Mutel, R. L.↗

NASA NTRS1985

High-angular resolution observations of stellar binary systems

A long-term program designed to investigate the spatial structure of centimetric radio emission from close binary systems using multistation VLBI array is discussed. Eleven binaries, including eight RS CVn systems, Algol, LSI 61 deg 303, and Cyg X-1, have been detected. The measured brightness temperatures vary from T(B) about 10 exp 8.5 K during periods of low activity to T(B) about 10 exp 10.5 K during flares. Extensive observation of a few sources has shown that the spatial structure is 'core-halo' with linear dimensions of about a stellar radius and the binary system, respectively. The observations are consistent with gyrosynchrotron emission of mildly relativistic electrons in magnetic fields of about 10 exp 1.5 + or - 0.5 gauss. The core sources appear to be optically thick, while the halo component is optically thin.

Lestrade, J.-F.↗

NASA NTRS1984

Detection of a sub-milliarcsecond radio component in the RS CVn system HR 1099

The RS CVn system HR 1099 was observed with a five station VLBI array at a frequency of 8.4 GHz during a strong radio outburst of approximately 400 mJy. The data are consistent with a circular Gaussian source of 0.8 + or - 0.12 milli-arcsec (FWHM), corresponding to a linear size of 4 + or - 0.6 x 10 to the 11th cm. This is comparable to the distance between the surfaces of the two stars, or to 75 percent of the diameter of the chromospherically active K star. Extrapolation of published photometric data shows that the starspot formation of HR 1099 was facing toward the observers at the times of observations. The high equivalent brightness temperature, approximately 10 billion K, is consistent with gyrosynchrotron emission from a power-law energy distribution of electrons in a magnetic field of strength about 30 gauss.

Mutel, R. L.↗

NASA NTRS1984

Very long baseline interferometry observations of the RS Canum Venaticorum system HR 5110 at 8.4 GHz

The RS CVn binary system HR 5110 was observed with a well-calibrated four-element VLBI array at a frequency of 8.4 GHz. The total flux density, which was nearly constant at 32 + or - 2 mJy, was monitored throughout the experiment with a 20 km baseline interferometer allowing accurate visibilities to be calculated. The observed visibilities are consistent with a source unresolved on all the baselines. The maximum size of the equivalent Gaussian source is 1.4 milli-arcsec (FWHM), corresponding to a linear size of 1.1 x 10 to the 12th cm at 52 pc. This maximum size is comparable with the overall size of the binary system. The inferred lower limit of the brightness temperature is 4 x 10 to the 8th K, which is higher than the coronal temperature of 10 to the 7th K measured in a soft X-ray survey. This is consistent with a nonthermal mechanism for the radiation process of the moderate radio outburst observed.

Mutel, R. L.↗

NASA NTRS1984

VLBI observations of the RS Canum Venaticorum binary systems UX Arietis and HR 1099 at 1.65 GHz

VLBI observations of the RS CVn binaries UX Arietis and HR 1099 have been made at 1.65 GHz using a three-element array with a minimum fringe spacing of 11.5 milli-arcsec. Both sources were found to be unresolved within measurement uncertainties. In both cases, the derived upper limit to the source size was comparable to the overall size of each binary system. The lower limits to the brightness temperature were 1.4 x 10 to the 10th K for UX Arietis and 2.9 x 10 to the 10th K for HR 1099. Simultaneous polarization measurements at the VLA showed 4-8 percent circular polarization and less than 2 percent linear polarization. It is found that the data are consistent with gyrosynchrotron emission from a power-law energy distribution of electrons in a magnetic field B less than or approximately equal to 6 gauss.

Mutel, R. L.↗