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All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Synchronization of magnetic stars in binary systems

Asynchronous rotation of magnetic stars in close binary systems drives substantial field-aligned electrical currents between the magnetic star and its companion. The resulting magnetohydrodynamic torque is able to account for the heretofore unexplained synchronous rotation of the strongly magnetic degenerate dwarf component in systems like AM Her, VV Pup, AN UMa, and EF Eri as well as the magnetic A type component in systems like HD 98088 and 41 Tauri. The electric fields produced by even a small asynchronism are large and may accelerate some electrons to high energies, producing radio emission. The total energy dissipation rate in systems with degenerate dwarf spin periods as short as 1 minute may reach 10 to the 33rd ergs/s. Total luminosities of this order may be a characteristic feature of such systems.

Lamb, F. K.↗
DOE OSTI2023

Tree-based solvers for adaptive mesh refinement code $\scriptsize{FLASH}$ – IV. An X-ray radiation scheme to couple discrete and diffuse X-ray emission sources to the thermochemistry of the interstellar medium

X-ray radiation, in particular radiation between 0.1 and 10 keV, is evident from both point-like sources, such as compact objects and T-Tauri young stellar objects, and extended emission from hot, cooling gas, such as in supernova remnants. The X-ray radiation is absorbed by nearby gas, providing a source of both heating and ionization. While protoplanetary chemistry models now often include X-ray emission from the central young stellar object, simulations of star-forming regions have yet to include X-ray emission coupled to the chemo-dynamical evolution of the gas. We present an extension of the $\scriptsize{TREERAY}$ reverse ray trace algorithm implemented in the flash magnetohydrodynamic code which enables the inclusion of X-ray radiation from 0.1 keV < E γ < 100 keV, dubbed $\scriptsize{XRAYTHESPOT}$. $\scriptsize{XRAYTHESPOT}$ allows for the use of an arbitrary number of bins, minimum and maximum energies, and both temperature-independent and temperature-dependent user-defined cross-sections, along with the ability to include both point and extended diffuse emission and is coupled to the thermochemical evolution. We demonstrate the method with several multibin benchmarks testing the radiation transfer solution and coupling to the thermochemistry. Finally, we show two example star formation science cases for this module: X-ray emission from protostellar accretion irradiating an accretion disc and simulations of molecular clouds with active chemistry, radiation pressure, and protostellar radiation feedback from infrared to X-ray radiation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1978

Copernicus observations of Ly-alpha and Mg II emission from HR 1099 /V711 Tauri/ and UX Ari

Ultraviolet observations of two RS CVn binaries obtained with Copernicus are described. High-resolution (0.05 A) U1 observations indicate that both HR 1099 and UX Ari display broad Ly-alpha emission. The Ly-alpha emission strength from HR 1099 is variable and seems to be correlated with orbital phase, while the UX Ari results indicate no significant variation. Moderate resolution (0.51 A) V2 scans of both systems show variable Mg II h and k emission-line profiles which usually matched the velocity of the more active star in each binary. Additionally, displaced emission components were seen at velocities of up to + or - 250 km/s, indicative of high-velocity gas motions. The radial velocities of these emission features from HR 1099 are marginally correlated with orbital phase. Highly active and variable chromospheric phenomena are found to be the most consistent explanation of these results.

Weiler, E. J.↗
NASA NTRS1974

Profiles of emission lines in Be stars. III

The long-period V/R emission variations in three Be stars, HD 20336, 25 Ori, and beta-one Mon have been studied according to the mathematical formulation of the eccentric rotating model presented in a previous paper. The predictions of the theory fit satisfactorily the general trend of observed data. Periods, eccentricities, and sizes of the emitting ring with respect to the stellar radius are thereby derived and found to be consistent with results of the previous investigation of 105 Tauri.

Albert, E.↗
NASA NTRS1994

Evidence for HCO(+) infall toward T Tauri?

High spectral and spatial resolution observations of the HCO(+) molecule toward the T Tau binary system obtained with the Owens Valley Millimeter Array reveal a broad emission line profile (V(sub LSR) = 7.2 km s(exp -1), Delta V = 2.0 km s(exp -1)) upon which a narrow, redshifted absorption feature (V(sub LSR) = 8.5 km s(exp -1), Delta V approximately equals 0.5 km s(exp -1)) is superposed. One possible interpretation of the absorption is that it rises from infall of molecular cloud envelope material onto the immediate circumbinary region, which would imply that large-scale dynamic accretion processes are still active well into the optically visible stages of star formation. Provided the mass is deposited at radii sufficiently close to the young stars, estimates of the accretion rates indicate that infall may add enough material to the system to account for the FU Orionis type flares recently observed in T Tau in approximately less than 100 yr.

Van Langevelde, Huib Jan↗
NASA NTRS2013

ALMA Observations of the Molecular Gas in the Debris Disk of the 30 Myr Old Star HD 21997

The 30 Myr old A3-type star HD 21997 is one of the two known debris dust disks having a measurable amount of cold molecular gas. With the goal of understanding the physical state, origin, and evolution of the gas in young debris disks, we obtained CO line observations with the Atacama Large Millimeter/submillimeter Array (ALMA). Here, we report on the detection of (12)CO and (13)CO in the J = 2-1 and J = 3-2 transitions and C(18)O in the J = 2-1 line. The gas exhibits a Keplerian velocity curve, one of the few direct measurements of Keplerian rotation in young debris disks. The measured CO brightness distribution could be reproduced by a simple star+disk system, whose parameters are r(sub in) < 26 AU, r(sub out) = 138 +/- 20 AU, Stellar M = 1.8 +0.5/−0.2 Solar M, and i = 32. Deg. 6 +/- 3 deg..1. The total CO mass, as calculated from the optically thin C(18)O line, is about (4-8) ×10(exp −2 ) Solar M, while the CO line ratios suggest a radiation temperature on the order of 6-9 K. Comparing our results with those obtained for the dust component of the HD 21997 disk from ALMA continuum observations by Moor et al., we conclude that comparable amounts of CO gas and dust are present in the disk. Interestingly, the gas and dust in the HD 21997 system are not colocated, indicating a dust-free inner gas disk within 55 AU of the star. We explore two possible scenarios for the origin of the gas. A secondary origin, which involves gas production from colliding or active planetesimals, would require unreasonably high gas production rates and would not explain why the gas and dust are not colocated. We propose that HD 21997 is a hybrid system where secondary debris dust and primordial gas coexist. HD 21997, whose age exceeds both the model predictions for disk clearing and the ages of the oldest T Tauri-like or transitional gas disks in the literature, may be a key object linking the primordial and the debris phases of disk evolution.

molecular gas↗
NASA NTRS1983

Spectroscopy of V711 Tauri (= HR 1099) - Fundamental properties and evidence for starspots

New orbital elements have been determined for the bright RS CVn-type system V711 Tau. The spectroscopic period has been refined to 2.83774 d + or - 0.00001 d. The eccentricity is determined to be 0.014 + or - 0.009, and the inclination of the system is 33 deg + or - 2 deg. The masses, radii, and equatorial rotational velocities for each component are stated.Evolutionary models suggest that mass transfer may begin in 70 to 80 million years. High SNR Reticon observations at red wavelengths show substantial differences in rotational velocity and line strength between the two components, as well as asymmetries in all absorption lines of the more massive, active, cooler star. These asymmetries are correlated with photometric variations and move across the line profiles with time. They are the result of starspot regions rotating in and out of view.

Fekel, F. C., Jr.↗
NASA NTRS1991

The extraordinary 1989 December 14/15 optical flare events on V711 Tauri

Photometry in B and V taken with the Vanderbilt Tennessee State 16 inch (41 cm) robotic telescope confirms the intense broad-band optical continuum flare activity reported by Chinese observers on the active chromosphere binary V711 Tau on December 14/15, 1989. Twelve hours after the flare reported from China, there occurred a separate and more intense flare with B and V amplitudes of 0.69 and 0.42 mag, respectively. These amplitudes correspond to peak flare luminosities of approximately 2 x 10 to the 33rd ergs/s in B and 1 x 10 to the 33rd ergs/s in V. The observed color of its excess light implies that the flaring region covered approximately 8 percent of the surface of the K1 subgiant star on which it erupted. Although the shape of the light curve was unchanged after the flare, the mean brightness of the star was enhanced by 3 percent in B, and it required nearly three months to decay to its preflare mean brightness. This is the first confirmed and, by far, the brightest example of broad-band optical flaring activity on an evolved, magnetically active star more luminous than the sun.

Henry, Gregory W.↗
NASA NTRS1993

Upper limits to the detection of ammonia from protoplanetary disks around HL Tauri and L1551-IRS 5

We present NH3(1, 1) and (2, 2) observations of the young stellar sources HL Tau and L1551-IRS 5 using the VLA in its B-configuration, which provides an angular resolution of about 0.4 arcsec (about 50 AU at 140 pc) at 1.3 cm wavelength. Our goal was to detect and resolve circumstellar molecular disks with radius of the order of 100 AU around these two sources. No ammonia emission was detected toward either of them. The 3-sigma levels were 2.7 mJy/beam and 3.9 mJy/beam for HL Tau and L1551-IRS 5, respectively, with a velocity resolution of about 5 km/s. With this nondetection, we estimate upper limits to the mass of the proposed protoplanetary molecular disks (within a radius of 10 AU from the central stars) on the order of 0.02/(X(NH3)/10 exp -8) solar mass for HL Tau and 0.1/(X(NH3)/10 exp -8) solar mass for L1551-IRS 5.

Gomez, Jose F.↗
NASA NTRS2011

Signposts of Planet Formation in the Disk of GM Aur

Rice et al. noted that transitional disks hosting massive Jovian-mass planets should have suppressed accretion onto the star, while bringing about an absence of silicate emission. Their models also predict systems with less massive planets should permit small grain dust and some gas to filter into the cavity, leaving larger grains confined to the outer disk. Such systems are expected to have polarized light originating within the cavity, silicate emission, and small-grain reflection nebulosity detectable in FUV high-contrast imagery. A further consequence is that molecular gas should be less abundant in the inner disk due to photodissociation by the stellar FUV radiation field. GM Aur is a T-Tauri star/transitional disk system, where both silicate emission and a 24 AU cavity has been detected. We continue the analysis of GM Aur with FUV and optical HST imagery and report the presence of small-grain reflection nebulosity detected from 1400 - 2000 A in the cavity region, as well as a molecular outflow that has an inner radius corresponding to the cavity wall. These data, together with the presence of silicate emission, suggest that GM Aur hosts a planet with likely mass between 1 and 5 Mass of Jupiter

Hornbeck, Jeremy↗
NASA NTRS2021

Multiwavelength Observations of the RV Tauri Variable System U Monocerotis: Long-term Variability Phenomena That Can Be Explained by Binary Interactions with a Circumbinary Disk

We present an X-ray through submillimeter observations of the classical RV Tauri(RVb-type)variable U Mon, apost-asymptotic giant branch(AGB)binary with a circumbinary disk(CBD). Our SMA observations indicate aCBD diameter of550 au. Our XMM-Newton observations make U Mon thefirst RV Tauri variable detected inX-rays. The X-ray emission is characteristic of a hot plasma(∼10 MK), withLX=5×1030erg s−1, and weconsider its possible origin from U Mon, its companion, and/or binary system interactions. Combining DASCHand AAVSO data, we extend the time-series photometric baseline back to the late 1880s andfind evidence thatU Mon has secular changes that appear to recur on a timescale of∼60 yr, possibly caused by a feature in the CBD.From literature radial velocities wefind that the binary companion is a∼2MeA-type main-sequence star. Theorientation of the binary’s orbit lies along our line of sight(ω=95°), such that apastron corresponds to photometricRVb minima, consistent with the post-AGB star becoming obscured by the near side of the CBD. In addition, wefind the size of the inner-CBD hole(∼4.5–9au)to be comparable to the binary separation, implying that one orboth stars may interact with the CBD at apastron. The obscuration of the post-AGB star implicates the companionas the likely source of the enhanced Hαobserved at RVb minima and of the X-ray emission that may arise fromaccreted material.

Laura D Vega↗
NASA NTRS1997

Ion Bombardment Experiments Suggesting an Origin for Organic Particles in Pre-Cometary and Cometary Ices

Simple molecules frozen as mantles of interstellar and circumstellar grains and incorporated into comets are subjected to ion bombardment in the form of cosmic rays, stellar flares, stellar winds, and ions accelerated in stellar wind shocks. The total expected dosage for the variety of situations range from 10 eV/molecule for interplanetary dust subjected to solar flares to 10(exp 6) eV/molecule for material in the T Tauri environment. Utilizing a Van de Graaff accelerator and a target chamber having cryogenic and mass spectrometer capabilities, we have bombarded frozen gases in the temperature range of 10 K to 30 K with 175 keV protons. After irradiation, removal of the ice by sublimation at an elevated temperature in vacuum reveals a fluffy residue. These experiments suggest that processes resulting in the formation of organic particles found in the coma of Comet Halley, "CHON", may have included ion bombardment. Also, the moderate energy (100 keV to 500 keV) shock accelerated ion environment of bipolar outflow of stars in the planetary nebula stage such as the Red Rectangle, could produce complex molecular species which emit the observed unidentified infrared bands at 3.3 micro-m, 6.2 micro-m, 7.7 micro-m, 8.6 micro-m, and 11.3 micro-m.

Wdowiak, Thomas J.↗
NASA NTRS1994

Detection of rotational modulation in the coronal extreme-ultraviolet emission from V711 Tauri?

The RS CVn binary V711 Tauri was observed by the Extreme Ultraviolet Explorer satellite (EUVE) twice during the latter half of 1992, for periods lasting several days. Light curves for the waveband 60-180 A derived from the all-sky survey scanning in August and from a pointed calibration observation made in October both exhibit a modulation of about 40%. The modulation in both data sets is very similar, with minimum flux occurring near orbital phase phi = 0.5. Analysis using a two-temperature optically thin plasma emission model reveals that most of the detected extreme ultraviolet (EUV) flux emanates from hot (approximately 10(exp 7) K) coronal plasma. The modulation is probably mostly due to either flare-like activity or to rotational occultation of a long-lived, compact, and especially bright coronal structure on the more active star of the system. The phased data support the latter hypothesis. This coronal structure is then likely to be associated with the presistent spot patterns seen on V711 Tau when using Doppler and photometric surface imaging techniques. Comparison with contemporaneous Stroemgren b-band photometry indicates that the optical minimum light leads the EUV maximum light by 90 deg in phase.

Drake, Jeremy J.↗
NASA NTRS1995

Starspot evolution, differential rotation, and magnetic cycles in the chromospherically active binaries lambda andromedae, sigma Geminorum, II Pegasi, and V711 Tauri

We have analyzed 15-19 yr of photoelectric photometry, obtained manually and with automated telescopes, of the chromospherically active binaries lambda And, sigma Gem, II Peg, and V711 Tau. These observations let us identify individual dark starspots on the stellar surfaces from periodic dimming of the starlight, follow the evolution of these spots, and search for long-term cyclic changes in the properties of these starspots that might reveal magnetic cycles analogous to the Sun's 11 yr sunspot cycle. We developed a computer code to fit a simple two-spot model to our observed light curves that allows us to extract the most easily determinable and most reliable spot parameters from the light curves, i.e., spot longitudes and radii. We then used these measured properties to identify individual spots and to chart their life histories by constructing migration and amplitude curves. We identified and followed 11 spots in lambda And, 16 in sigma Gem, 12 in II Peg, and 15 in V711 Tau. Lifetimes of individual spots ranged from a few months to longer than 6 yr. Differential rotation coefficients, estimated from the observed range of spot rotation periods for each star and defined by equation (2), were 0.04 for lambda And, 0.038 for sigma Gem, 0.005 for II Peg, and 0.006 for V711 Tau, versus 0.19 for the Sun. We searched for cyclic changes in mean brightness, B-V color index, and spot rotation period as evidence for long-term cycles. Of these, long-term variability in mean brightness appears to offer the best evidence for such cycles in these four stars. Cycles of 11.1 yr for lambda And, 8.5 yr for sigma Gem, 11 yr for II Peg, and 16 yr V711 Tau are implied by these mean brightness changes. Cyclic changes in spot rotation period were found in lambda And and possibly II Peg. Errors in B-V were too large for any long-term changes to be detectable.

Henry, Gregory W.↗
NASA NTRS2012

PDS 144: The First Confirmed Herbig Ae-Herbig Ae Wide Binary

PDS 144 is a pair of Herbig Ae stars that are separated by 5.35" on the sky. It has previously been shown to have an A2Ve Herbig Ae star viewed at 83 deg inclination as its northern member and an A5Ve Herbig Ae star as its southern member. Direct imagery revealed a disk occulting PDS 144 N - the first edge-on disk observed around a Herbig Ae star. The lack of an obvious disk in direct imagery suggested PDS 144 S might be viewed face-on or not physically associated with PDS 144 N. Multi-epoch HST imagery of PDS 144 with a 5 yr baseline demonstrates PDS 144 N & S are comoving and have a common proper motion with TYC 6782-878-1. TYC 6782-878-1 has previously been identified as a member of Upper Sco sub-association A at d = 145 +/- 2 pc with an age of 5 - 10 Myr. Ground-based imagery reveals jets and a string of HH knots extending 13' (possibly further) which are aligned to within 7 deg +/- 6 deg on the sky. By combining proper motion data and the absence of a dark mid-plane with radial velocity data, we measure the inclination of PDS 144 S to be i = 73 deg +/- 7 deg. The radial velocity of the jets from PDS 144 N & S indicates they, and therefore their disks, are misaligned by 25 deg +/- 9 deg.. This degree of misalignment is similar to that seen in T-Tauri wide binaries.

Hornbeck, J. B.↗
NASA NTRS1995

Spectroscopic detection of the secondaries of the Hyades interferometric spectroscopic binary theta(sup 2) Tauri and of the interferometric spectroscopic binary alpha Andromedae

We report new high-resolution, wide-wavelength-coverage CCD observations of the visual and near-infrared spectra of the interferometric spectroscopic binaries theta(sup 2) Tau (primary spectral type A 7 III) and alpha And (primary spectral type B8 IVpMnHg), which allow the first direct spectroscopic detection of their secondaries. We have measured primary and secondary radial velocities and used them to redetermine the spectroscopic orbits of the primaries, make an improved determination of K(sub 2) for theta(sup 2) Tau, and measure K(sub 2) for alpha And for the first time. The spectroscopic orbits combined with the interferometrically measured visual orbits of theta(sup 2) Tau and alpha And provide masses and distances, M(sub 1) = 2.1 +/- 0.3 solar mass, M(sub 2) = 1.6 +/- 0.2 solar mass, and d = 44.1 +/- 2.2 pc for theta(sup 2) Tau and M(sub 1) = 5.5 +/- 0.5 solar mass, M(sub 2) = 2.3 +/- 0.2 solar mass, and d = 34.0 +/- 1.3 pc for alpha And. The distance to theta(sup 2) Tau and a foreground correction of 0.07 +/- 0.05 mag set the distance to the center of the Hyades cluster at 45.5 +/- 2.5 pc, or m - M = 3.29 +/- 0.12. Indirect estimates of the mass of theta(sup 2) Tau's primary, made via the mass-luminosity relation and via the Hyades cluster turnoff mass, are consistent with these dynamical masses for its primary and secondary. But in the case of alpha And, the mass-luminosity relation suggests that our dynamical masses for its primary and secondary may be too large. For alpha And somewhat smaller dynamical masses (4.0 and 1.9 solar mass) and the correspondingly smaller distance (31 pc), required by the corresponding larger orbital parallax, provide results consistent with the mass-luminosity relation for normal stars.

Tomkin, Jocelyn↗