Physical conditions in a quiescent prominence derived from UV spectra obtained with the UVSP instrument on the SMM

A quiescent prominence observed above the north-west limb on November 20, 1980, is analyzed using data obtained with the Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission (SMM). The spectral data include the lines 1215 Å of Hi, 1401 Å of Oiv, 1402 Å of Siiv, 1548 Å of Civ, 1640 Å of Hei, and 1655 Å of Ci. From an analysis of these lines and their emission patterns we deduce physical characteristics of the prominence plasma, and suggest in particular that the prominence consisted of flux tubes at various temperatures. In the hotter parts of the plasma the number density reached values of about 3 × 10¹¹ cm^#X2212;3.     

Variability and possible rapid evolution of the hot post-AGB stars Hen 3-1347, Hen 3-1428, and LSS 4634

We present the results of spectroscopic and photometric observations for three hot southern-hemisphere post-AGB objects, Hen 3-1347 = IRAS 17074-1845, Hen 3-1428 = IRAS 17311-4924, and LSS 4634 = IRAS 18023-3409. In the spectrograms taken with the 1.9-m telescope of the South African Astronomical Observatory (SAAO) in 2012, we have measured the equivalent widths of the most prominent spectral lines. Comparison of the new data with those published previously points to a change in the spectra of Hen 3-1428 and LSS 4634 in the last 20 years. Based on ASAS data, we have detected rapid photometric variability in all three stars with an amplitude up to 0 _· ^m 3-0 _· ^m 4 in the V band. A similarity between the patterns of variability for the sample stars and other hot protoplanetary nebulae is pointed out. We present the results of UBV observations for Hen 3-1347, according to which the star undergoes rapid irregular brightness variations with maximum amplitudes ΔV = 0 _· ^m 25, ΔB = 0 _· ^m 25, and ΔU = 0 _· ^m 30 and shows color-magnitude correlations. Based on archival data, we have traced the photometric history of the stars over more than 100 years. Hen 3-1347 and LSS 4634 have exhibited a significant fading on a long time scale. The revealed brightness and spectrum variations in the stars, along with evidence for their enhanced mass, may be indicative of their rapid post-AGB evolution.     

Spectral analysis of the optical continuum in the 24 April 1981 flare

Spectrograph and multiple-band polarimeter observations of the 24 April 1981 white-light flare indicate the presence of an optical continuum with intensity increasing strongly below 4000 Å. The flare emission (lines and continuum combined) is unpolarized and, at 3600 Å, exceeds the brightness of the background solar surface by 360%. Analysis of the spectrum between 3600 and 8200 Å, at a location three arc sec from the brightest point in the kernel, yields a probable temperature of 6700 K for the continuum emitting layer. The wavelength dependence of the continuum indicates emission by both negative hydrogen (H^?) and Balmer continuum, with the H^? probably originating in the upper photosphere at a height (above τ_{5000 Å} = 1) in the range 200–300 km. Analysis of the Balmer lines and continuum yields an electron density 5.3 × 10¹³ cm^?3 and a second-level hydrogen column density 1.1 × 10¹⁶ cm^?2. The peak radiative output integrated over wavelength is 6.1 × 10²⁷ erg s^?1. The observed continuum intensity, if originating at a height of 300 km, implies an energy loss rate of 10³ erg s^?1 cm^?3.     

The symbiotic binary system EG Andromedae

Photometric observations of the symbiotic star EG and confirm that the binary system is eclipsing. The epoch of primary minimum is computed. The new period 474 days instead of 470 days is estimated by a comparison of line profiles of Balmer lines taken in 1967–69 and 1982–84. The new ephemeris is 1 $$JD_{min.} = 2 446 336.7 + 474 E.$$      

A dynamo theory of solar flares

It is proposed that the solar flare phenomenon can be understood as a manifestation of the electrodynamic coupling process of the photosphere-chromosphere-corona system as a whole. The system is coupled by electric currents, flowing along (both upward and downward) and across the magnetic field lines, powered by the dynamo process driven by the neutral wind in the photosphere and the lower chromosphere. A self-consistent formulation of the proposed coupling system is given. It is shown in particular that the coupling system can generate and dissipate the power of 10²⁹ erg s^#X2212;1 and the total energy of 10³² erg during a typical life time (10³ s) of solar flares. The energy consumptions include Joule heat production, acceleration of current-carrying particles along field lines, magnetic energy storage and kinetic energy of plasma convection. The particle acceleration arises from the development of field-aligned potential drops of 10–150 kV due to the loss-cone constriction effect along the upward field-aligned currents, causing optical, X-ray and radio emissions. The total number of precipitating electrons during a flare is shown to be of order 10³⁷–10³⁸.     

Cosmogenic Isotope Variability During the Maunder Minimum: Normal 11-year Cycles Are Expected

The amplitude of the 11-year cycle measured in the cosmogenic isotope ¹⁰Be during the Maunder Minimum is comparable to that during the recent epoch of high solar activity. Because of the virtual absence of the cyclic variability of sunspot activity during the Maunder Minimum this seemingly contradicts an intuitive expectation that lower activity would result in smaller solar-cycle variations in cosmogenic radio-isotope data, or in none, leading to confusing and misleading conclusions. It is shown here that large 11-year solar cycles in cosmogenic data observed during periods of suppressed sunspot activity do not necessarily imply strong heliospheric fields. Normal-amplitude cycles in the cosmogenic radio-isotopes observed during the Maunder Minimum are consistent with theoretical expectations because of the nonlinear relation between solar activity and isotope production. Thus, cosmogenic-isotope data provide a good tool to study solar-cycle variability even during grand minima of solar activity.     

The shape of the small satellites of Saturn: Gravitational equilibrium vs solid-state strength

In the set of small satellites of Saturn recently imaged by the Voyager probes, we can observe the transition from irregularly-shaped, strength-dominated objects to larger, gravity-dominated bodies with shapes roughly fitting the theoretical equilibrium figures. The transition occurs for a radius of 100±50 km, corresponding to a typical material strength of the order of 10⁷ dynes cm^?2. We discuss briefly the cases of Mimas, Enceladus, Hyperion, Phoebe and the small coorbital and F-ring shepherding moons, showing that an analysis of the shape data can often provide interesting results on the physical properties, origin and collisional history of these objects.     

Interpretation of vector magnetograph data including magneto-optic effects

In this paper, the presence of Faraday rotation in measurements of the orientation of a sunspot's transverse magnetic field is investigated. Using observations obtained with the Marshall Space Flight Center's (MSFC) vector magnetograph, the derived vector magnetic field of a simple, symmetric sunspot is used to calculate the degree of Faraday rotation in the azimuth of the transverse field as a function of wavelength from analytical expressions for the Stokes parameters. These results are then compared with the observed rotation of the field's azimuth which is derived from observations at different wavelengths within the Fei 5250 Å spectral line. From these comparisons, we find: the observed rotation of the azimuth is simulated to a reasonable degree by the theoretical formulations if the line-formation parameter η _o is varied over the sunspot; these variations in η _o are substantiated by the line-intensity data; for the MSFC system, Faraday rotation can be neglected for field strengths less than 1800 G and field inclinations greater than 45°; to minimize the effects of Faraday rotation in sunspot umbrae, MSFC magnetograph measurements must be made in the far wings of the Zeeman-sensitive spectral line.     

Areas of Polar Coronal Holes from 1996 Through 2010

Polar coronal holes (PCHs) trace the magnetic variability of the Sun throughout the solar cycle. Their size and evolution have been studied as proxies for the global magnetic field. We present measurements of the PCH areas from 1996 through 2010, derived from an updated perimeter-tracing method and two synoptic-map methods. The perimeter-tracing method detects PCH boundaries along the solar limb, using full-disk images from the SOlar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT). One synoptic-map method uses the line-of-sight magnetic field from the SOHO/Michelson Doppler Imager (MDI) to determine the unipolarity boundaries near the poles. The other method applies thresholding techniques to synoptic maps created from EUV image data from EIT. The results from all three methods suggest that the solar maxima and minima of the two hemispheres are out of phase. The maximum PCH area, averaged over the methods in each hemisphere, is approximately 6 % during both solar minima spanned by the data (between Solar Cycles 22/23 and 23/24). The northern PCH area began a declining trend in 2010, suggesting a downturn toward the maximum of Solar Cycle 24 in that hemisphere, while the southern hole remained large throughout 2010.     

Alpha Cygni as a radial-velocity variable

One hundred and twentythree radial velocities for α Cyg are derived between December 1977 and October 1982. These photospheric velocities are derived from N_I lines near 8700 å. Semiregular variations in radial velocities are present with periods of 7 to 20 days. The range of variation of 14.3 kms^?1 observed in the present radial velocities of α Cyg is close to the sum of the amplitudes (10.44 kms^?1) of all the pulsation periods from 7 to 101 days (Lucy 1976a) and is also approximately equal to micro and macro-turbulent velocities.     

Problems with non-thermal models for the narrow line gamma rays reported from SS 433

The jet/grain model proposed by Ramatyet al. (1984, hereafter abbreviated as RKL) for production of the narrow gamma-ray lines reported from SS433 is examined and shown to be untenable on numerous grounds. Most importantly:

1. The huge Coulomb collisional losses (W _c?2×10⁴¹ erg s^?1) from the jet, which would necessarily accompany non-thermal production of the gamma rays, demands a jet acceleration/collimation process acting over a very long range and with a power at least 10² times the Eddington limit for any stellar object.
2. There is a collisional thick target limit (irrespective of jet mass) to the gamma ray yield per interstellar proton. Consequently, the gamma-ray data demand an improbably high interstellar density (?10⁹ cm^?3).
3. For the grains to be kept cool enough (?3000 K) to survive the heating rateW _c either by radiation or jet expansion would demand a ‘jet’ wider than its length and so inconsistent with narrow lines. In the case of radiative cooling, the resultant IR flux would exceed the observed values by a factor ?10⁴.
4. Light scattered on the jet grain mass required would be highly polarized, contrary to observations, unless the jet was optically thick to grains, again precluding their radiative cooling.
5. To avoid unacceptable precessional broadening of the gamma-ray lines demands an emitting jet length ?0.5 days atv=0.26c. This increases the necessary mass loss rate by a factor ?10 over the values obtained by RKL who assumed a 4-day ‘flare’.
6. The model also predicts rest energy gamma-ray lines which are not observed.

     

The properties of coronal voids

Observations of the outer solar corona obtained by the High Altitude Observatory's coronagraph aboard Skylab reveal the presence of dark, ray-like structures in the corona. A systematic identification of these voids, which exist for periods of about 24 hr, is presented and their existence as a coronal phenomenon, as opposed to a subtle photographic effect, verified. Photometric analysis indicates that these features represent reductions in the coronal radiance on the order of 5% - or about 2–3 × 10^?10 B _⊙ at 3 R _⊙. The use of a previously determined model of the electron component of the corona permits specification of the electron density in the voids over the range 2.5–4.5 R _⊙. In spite of the inevitable uncertainties regarding their longitudinal extent, we estimate that their electron density is comparable to, or less than, that in coronal holes at similar heights. Projection of the phenomena onto synoptic surface maps indicates a close relationship with filaments and neutral lines; a potentially significant temporal correlation between the void formation and that of the underlying prominence is noted. The spatial and temporal resolution of the data set places stringent restrictions on any model which may be used to infer the physical processes of formation or decay of voids; several possibilities are suggested which involve either changes in the coronal base temperature or the magnetic flux.     

THz photometers for solar flare observations from space

The search for the still unrevealed spectral shape of the mysterious THz solar flare emissions is one of the current most challenging research issues. The concept, fabrication and performance of a double THz photometer system, named SOLAR-T, is presented. Its innovative optical setup allows observations of the full solar disk and the detection of small burst transients at the same time. The detecting system was constructed to observe solar flare THz emissions on board of stratospheric balloons. The system has been integrated to data acquisition and telemetry modules for this application. SOLAR-T uses two Golay cell detectors preceded by low-pass filters made of rough surface primary mirrors and membranes, 3 and 7 THz band-pass filters, and choppers. Its photometers can detect small solar bursts (tens of solar flux units) with sub second time resolution. Tests have been conducted to confirm the entire system performance, on ambient and low pressure and temperature conditions. An artificial Sun setup was developed to simulate performance on actual observations. The experiment is planned to be on board of two long-duration stratospheric balloon flights over Antarctica and Russia in 2014–2016.     

Photometric and polarimetric studies of three W UMa-type binaries: FZ Ori,V407 Peg and LP UMa

We present analyses of new optical photometric observations of three W UMa-type contact binaries FZ Ori, V407 Peg and LP UMa. Results from the first polarimetric observations of the FZ Ori and V407 Peg are also presented. The periods of FZ Ori, V407 Peg and LP UMa are derived to be 0.399986, 0.636884 and 0.309898 d, respectively. The O?C analyses indicate that the orbital periods of FZ Ori and LP UMa have increased with the rate of 2.28×10^?8 and 1.25×10^?6 d?yr^?1, respectively and which is explained by transfer of mass between the components. In addition to the secularly increasing rate of orbital period, it was found that the period of FZ Ori has varied in sinusoidal way with oscillation period of ～30.1 yr. The period of oscillations are most likely to be explained by the light-time effect due to the presence of a tertiary companion. Small asymmetries have been seen around the primary and secondary maxima of light curves of all three systems, which is probably due to the presence of cool/hot spots on the components. The light curves of all three systems are analysed by using Wilson-Devinney code (WD) and the fundamental parameters of these systems have been derived. The present analyses show that FZ Ori is a W-subtype, and V407 Peg and LP UMa are A-subtype of the W UMa-type contact binary systems. The polarimetric observations in B, V, R and I bands, yield average values of polarization to be 0.26±0.03, 0.22±0.02, 0.22±0.03 and 0.22±0.05 per cent for FZ Ori and 0.21±0.02, 0.29±0.03, 0.31±0.01 and 0.31±0.04 per cent for V407 Peg, respectively.     

On the heat flow of a gravitationally-differentiated moon of fission origin

It is shown that the mean value for the heat flow of a gravitationally-differentiated Moon of fission origin is about 13 erg cm^?2 s^?1 and that the heat flow varies regionally from about 3 erg cm^?2s^?1 to more than 45 erg cm^?2s^?1. These regional variations in the heat flow are caused by a non-uniform distribution of K, U and Th in the KREEP zone at the crust-upper mantle boundary and the redistribution of crustal materials and K, U and Th rich KREEP materials by basin-forming impacts. The scale of these regional variations is hundreds of km. The models presented are in accord with the Apollo 15 and 17 heat flow measurements.     

Physical parameters of the Orion Bar photodissociation region from radio recombination line observations at 8 mm

Observations of carbon (C), hydrogen and helium (H, He) radio recombination lines (RRLs) at four positions in the Orion Bar photodissociation region (PDR) and toward the center of Orion A have been performed with the RT-22 radio telescope (Pushchino) at 8 mm. The physical parameters of the PDR at these points have been estimated by comparing the carbon RRLs and infrared CII and OI lines. A hydrogen number density in the range 1.2–3.1 × 10⁵ cm^?3 and a mean size of the region along the line of sight (L) in the range 0.006–0.04 pc have been derived. The PDR temperature decreases with increasing distance from the exciting star (θ ¹ C Ori) from 210–230 to 140–150 K (a distance of ≈5′). The data obtained confirm the increase in the PDR size along the line of sight toward the Orion Bar, where, however, L has turned out to be less than the available values in the literature, which can be explained by the presence of clumps in the PDR. A density jump is evident in the Orion Bar region. The PDR zone encompasses the core of the HII region by a thin layer and extends farther, delineating the boundary and the ionization front of the core of the HII region in the Orion Bar and further out the boundary between the halo of the HII region and the molecular cloud. The derived emission measure (EM) toward the Orion Bar has been compared with other C RRL observations. The EM measured from carbon RRLs is EM ≈ 100(±50%) pc cm^?6, imposing constraints on the possible two-component PDR structure. Estimates show that the star θ ¹ C Ori is quite sufficient as a carbon ionization source in the Orion Bar PDR. Some of the data on the ionized hot gas (HII) in this direction have been obtained from H and He RRLs. In particular, the radial velocities (V _lsr) of the HII region are blueshifted with respect to V _lsr of the PDR by 10–17 km s^?1, while the relative ionized helium abundance decreases with increasing distance from the star, indicating that the helium ionization zone is smaller than the ionized hydrogen one.     

Observation of the flare of 12 June 1982 by Norikura coronagraph and Hinotori

Flare activity was observed near the limb with two coronagraphs at the Norikura Solar Observatory and the Soft X-ray Crystal Spectrometer (SOX) aboard HINOTORI. A prominence activation occurred and then Hα brightenings were seen on the disk near the prominence. The prominence became very bright and its electron density increased to 10^12.8 cm^?3 in 1/2 hour. Loop prominence systems appeared above the Hα brightenings about half an hour after the onset of the flare, and were observed in the coronal lines CaXV 5694Å, FeXIV 5303Å, and FeX 6374Å. Shifted and asymmetric profiles of the emission line of 5303Å were sometimes observed, and turbulent phenomena occurred even in the thermal phase. The energy release site of the flare at the onset would be lower than 20 000 km above the solar limb.