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Aims. We aim to investigate how polarimetric observations can improve our understanding of the nature and diversity of M/X-type asteroids. Methods. Polarimetric observations of the selected M/X-type asteroids were carried out at the Tohoku 0.6-m telescope at Haleakala Observatory, Hawaii (simultaneously in BVR filters), the 2-m telescope of the Bulgarian National Astronomical Observatory in Rozhen (in R filter), and the 2.15-m telescope of the Complejo Astron\'omico El Leoncito (CASLEO), Argentina (in V filter). We analysed the polarimetric characteristics of M/X-type asteroids along with the available data obtained by other techniques. Results. New polarimetric observations of 22 M/X-type asteroids combined with published observations provide a data set of 41 asteroids for which the depth of a negative polarisation branch and/or inversion angle were determined. We found that the depth of the negative polarisation branch tends to increase with decreasing steepness of the near-infrared spectra. Asteroids with a deeper negative polarisation branch tend to have a higher radar circular polarisation ratio. We show that, based on the relationship of the depth of the negative polarisation branch and inversion angle, two main sub-types can be distinguished among M-type asteroids. We suggest that these groups may be related to different surface compositions similar to (1) irons and stony-irons and (2) enstatite and iron-rich carbonaceous chondrites., Comment: 11 pages, 6 figures, 2 tables

Measurements of starlight polarized by aligned interstellar dust grains are used to probe the relation between the orientation of the ambient interstellar magnetic field (ISMF) and the ISMF traced by the ribbons of energetic neutral atoms discovered by the Interstellar Boundary Explorer spacecraft. We utilize polarization data, many acquired specifically for this study, to trace the configuration of the ISMF within 40 pc. A statistical analysis yields a best-fit ISMF orientation, B magpol, aligned with Galactic coordinates ℓ = 42°, b = 49°. Further analysis shows the ISMF is more orderly for “downfield” stars located over 90° from B magpol. The data subset of downfield stars yields an orientation for the nearby ISMF at ecliptic coordinates λ, β ≈ 219° ± 15°, 43° ± 9° (Galactic coordinates l, b ≈ 40°, 56°, ±17°). This best-fit ISMF orientation from polarization data is close to the field direction obtained from ribbon models. This agreement suggests that the ISMF shaping the heliosphere belongs to an extended ordered magnetic field. Extended filamentary structures are found throughout the sky. A previously discovered filament traversing the heliosphere nose region, “Filament A,” extends over 300° of the sky, and crosses the upwind direction of interstellar dust flowing into the heliosphere. Filament A overlaps the locations of the Voyager kilohertz emissions, three quasar intraday variables, cosmic microwave background (CMB) components, and the inflow direction of interstellar grains sampled by Ulysses and Galileo. These features are likely located in the upstream outer heliosheath where ISMF drapes over the heliosphere, suggesting Filament A coincides with a dusty magnetized plasma. A filament 55° long is aligned with a possible shock interface between local interstellar clouds. A dark spot in the CMB is seen within 5° of the filament and within 10° of the downfield ISMF direction. Two large magnetic arcs are centered on the directions of the heliotail. The overlap between CMB components and the aligned dust grains forming Filament A indicates the configuration of dust entrained in the ISMF interacting with the heliosphere provides a measurable foreground to the CMB.

We present the results of our power spectral density analysis for the BL Lac object OJ\,287, utilizing the {\it Fermi}-LAT survey at high-energy $\gamma$-rays, {\it Swift}-XRT in X-rays, several ground-based telescopes and the {\it Kepler} satellite in the optical, and radio telescopes at GHz frequencies. The light curves are modeled in terms of continuous-time auto-regressive moving average (CARMA) processes. Owing to the inclusion of the {\it Kepler} data, we were able to construct \emph{for the first time} the optical variability power spectrum of a blazar without any gaps across $\sim6$ dex in temporal frequencies. Our analysis reveals that the radio power spectra are of a colored-noise type on timescales ranging from tens of years down to months, with no evidence for breaks or other spectral features. The overall optical power spectrum is also consistent with a colored noise on the variability timescales ranging from 117 years down to hours, with no hints of any quasi-periodic oscillations. The X-ray power spectrum resembles the radio and optical power spectra on the analogous timescales ranging from tens of years down to months. Finally, the $\gamma$-ray power spectrum is noticeably different from the radio, optical, and X-ray power spectra of the source: we have detected a characteristic relaxation timescale in the {\it Fermi}-LAT data, corresponding to $\sim 150$\,days, such that on timescales longer than this, the power spectrum is consistent with uncorrelated (white) noise, while on shorter variability timescales there is correlated (colored) noise., Comment: ApJ accepted

Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects of certain hereditary contributions to GW emission are required to predict impact flare timings of OJ 287. We develop an approach that incorporates this effect into the binary black hole model for OJ~287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the binary black hole central engine model. The deduced rate of orbital period decay is nine orders of magnitude higher than the observed rate in PSR 1913+16, demonstrating again the relativistic nature of OJ 287's central engine. Finally, we argue that precise timing of the predicted 2019 impact flare should allow a test of the celebrated black hole "no-hair theorem" at the 10% level., 24 pages, 11 figures, 3 tables, accepted for publication in ApJ

We present new UBVRIpolarization measurements of the interacting Be binary CX Dra. On time scale of several weeks polarization variations clearly correlate with the binary orbital motion. Long term changes in polarization are seen in the course of several months. Analysis of the periodic component of polarization gives orbital inclination i � 73 ◦ which is substantially higher than values previously reported in the literature (55 ◦ ). Our two datasets obtained about 9 months apart reveal significant changes in the distribution of the scattering material of the circumbinary envelope.

We report linear polarization measurements of a set of symbiotic stars, made at several epochs during the period 1994-1998. Evidence of intrinsic polarization is looked for from the wavelength dependence of the polarization degree and position angle in UBVRI bands. The results have also been analysed to search for temporal variability of polarization. Several objects have shown a polarization spectrum different from that produced by interstellar dust grains and/or polarimetric variations on time scales as short as several days or months, indicating the presence of polarization component of circumstellar origin., Facultad de Ciencias Astronómicas y Geofísicas

We report the optical identification of RE 2107-05, a new EUV source discovered in the ROSAT Wide Field Camera all-sky survey, and present the results of subsequent follow-up observations. The optical counterpart of RE 2107-05 is identified spectroscopically with a 15-mag star that has an emission-line spectrum characteristic of magnetic cataclysmic variables. Using subsequent photometry and polarimetry, we demonstrate that the counterpart shows strong and variable circular polarization, confirming this to be an AM Her system. The polarimetry and photometry are modulated at a period of 125 min, and the optical light curve shows an eclipse with a complex, wavelength-dependent profile

Five-colour (UBVRI) polarimetric observations of a sample of solar-type stars are reported. The observations show a clear wavelength dependence of polarization for a few stars, and a statistical dependence on activity (CaII(H+K)-emission) in the short wavelengths (U and B). Recent observations on successive nights show also rotational variations of linear polarization in U or B band for some stars. These observations indicate large spotty areas and/or scattering patches on these stars.

For a sample of RS CVn binaries Busso and collaborators (Busso et al. , 1987, 1988; Busso and Scaltriti, 1990) compared the observed energy distribution from the UV to the near-IR (and to IRAS bandpasses for some objects) with those calculated from the known radii and spectral types of the stellar components. About 25% of the sample gave evidence of an IR excess up to 0.7 mag, generally starting from the I-band. The excess is significantly larger than observational error. These same authors ascribe the excess to a thin dust shell surrounding the binary. Using the “dirty silicates” model by Jones and Merrill (1976) they find for the shell a temperature range of 1500 K to 2000 K, an optical depth of about 0.01 at 10 micrometers in the shell, and a distance of the shell from the stars to be typically about 100 times the radius of the larger star.

We report on UBVRI polarimetry of the recently identified Intermediate Polar 1WGA J1958.2+3232, carried out on 2000 August, 4-6 at the Nordic Optical Telescope. Circular polarization was detected in R and I bands with an increasing absolute mean value with wavelength. There is evidence of possible modulation of the circular polarization at twice the previously reported white dwarf spin period, suggesting that it is the true period and that the modulation in optical and X-ray is dominated by the first harmonic. Indication of modulation at the orbital period is also present., Comment: 4 pages, 6 figures, accepted by A&A; editing changes only

HERBIG Ae/Be objects are young stars of intermediate mass (3–5 solar masses) surrounded by reflection nebulae composed of dust and gas remaining from the star-forming cloud1–3. Scattering by dust particles strongly polarizes light from the circumstellar nebula. Using imaging polarimetry in excellent conditions of atmospheric seeing (0.4 arcsec) from the La Palma observatory, we have resolved an optically thick disk around the Herbig Ae/Be object V376 Cassiopeiae. Its effective radius increases from 0.8 arc-sec in the near infrared (∼1 μm wavelength) to 1.2 arcsec at optical wavelengths (∼550 nm) because of the higher opacity of the disk material at shorter wavelengths. The corresponding linear disk radius is 500–750 AU, about an order of magnitude larger than our Solar System. The polarization behaviour within a 0.5-arcsec diameter circle around the companion star V633 Cas suggests the presence of a more compact (

For a sample of RS CVn binaries Busso and collaborators (Busso et al., 1987, 1988; Busso and Scaltriti, 1990) compared the observed energy distribution from the UV to the near-IR (and to IRAS bandpasses for some objects) with those calculated from the known radii and spectral types of the stellar components. About 25% of the sample gave evidence of an IR excess up to 0.7 mag, generally starting from the I-band. The excess is significantly larger than observational error. These same authors ascribe the excess to a thin dust shell surrounding the binary. Using the “dirty silicates” model by Jones and Merrill (1976) they find for the shell a temperature range of 1500 K to 2000 K, an optical depth of about 0.01 at 10 micrometers in the shell, and a distance of the shell from the stars to be typically about 100 times the radius of the larger star.

We have discovered a bright (V ~ 14.5) cataclysmic variable during observations of the soft X-ray sources in the list of Singh et al. The optical source, which is coincident with the X-ray position of WGA J1802.1+1804, shows all the characteristics of a magnetic AM Herculis-type system: circular polarization, He II strength greater than Hβ, multiple line components, and a consistent photometric, polarimetric, spectroscopic, and X-ray period of 113 minutes. The X-ray spectrum shows a dominant soft blackbody (kT = 20-45 eV) and a weaker bremsstrahlung component (kT > 1 keV), while the circular polarization is relatively low (4% in the red).

A new ultrasoft X-ray source, WGA J1047.1+6335, was discovered during a search of the ROSAT PSPC pointed observations, data from which are publicly available (White, Giommi, & Angelini; Singh et al.). We identify the X-ray source with an optical object of V 19.4 mag in the error circle of the X-ray source position. Optical and X-ray photometry has revealed the presence of an ~40 minute period. Strong emission lines of H and He have been detected in its optical spectrum. The X-ray spectrum of WGA J1047.1+6335 is best fitted with a blackbody (kT 40-50 eV) with negligible interstellar absorption and no X-rays with energies greater than 0.5 keV. Polarimetry shows a high amplitude (20% circular polarization) variation on an 80 minute timescale. These properties all suggest a polar with an 80 minute orbital period and either beaming/self-eclipsing effects from one pole or nearly equal emission from two poles.

We report the discovery of very strong variable (+50 to -20 %) circular polarization in the ROSAT EUV source RE 1307+535 in the red (600–710 nm) spectral region. The amplitude and the peak value of the broad-band circular polarization are the largest observed so far in any astrophysical object. The high degree of polarization requires that the observed red band flux of RE 1307+535 is dominated by cyclotron emission from a rather homogeneous region with little spread in the field strength and direction. Relative contributions from unpolarized (thermal) radiation sources are unusually small. We have modelled the observed circular polarization variation over the 79.7 min spin period of the white dwarf with the inclination of the spin axis i~75°, and two emission regions near the opposite magnetic poles, displaced 30–50° from the rotational poles.

Data of our on-going program on the interstellar polarization in the Small Magellanic Cloud (SMC) seem to show a correlation between the UV extinction and the parameters of the Serkowski law which describe the polarization. Fits of popular interstellar dust models to the polarization data are not always satisfactory, being better for stars with small wavelength of maximum polarization, λmax.

The sample of Ae/Be stars listed by Herbig (1960) are prime candidates for early-type, pre-Main Sequence stars. Their characteristics, as described by Herbig (1960) and the spectroscopic studies by Strom et al. (1972) and by Garrison and Anderson (1977), indicate that the objects are young with features such as emission lines, association with dust clouds and reflection nebulosity, irregular variability, infrared excess and molecular line emission. These objects are recognized as representing a group of higher-mass analogs of the T Tauri stars.

Our simultaneous five-colour (UBVRI) linear and circular polarimetry of PG 1031+234 have revealed a strong rotationally modulated circular polarization, peaking in the ultraviolet (Pmax(U)∼−17%)

Five symbiotic stars have been observed for linear polarization (UBVRI) in September 1981. Three systems, CH Cyg, CI Cyg and AG Peg show intrinsic polarization while in the case of Z And and AX Per the observed polarization seems to be mostly of interstellar origin. The position angle of polarization of CI Cyg and AG Peg rotates strongly vs. wavelength, as observed also for CH Cyg in 1977-80. The polarization of CH Cyg has decreased since May 1980, especially in the I, R and U bands, so that the maximum polarization is now in the blue (PB ~ 0.3 %). Probably we are monitoring the formation, growth and disappearance of dust particles in the atmosphere of this star. Two related systems, PU Vul (Nova Vul 1979) and R Aql (Mira) have polarization behaviour rather similar to that of symbiotic stars which suggests that the M type giant present in these systems is responsible for most of the intrinsic polarization.

We present the first observations of the AM Her type object EF Eri where both the polarization and the photometric data are recorded simultaneously in five color bands (UBVRI). The position angle rotates strongly (~30° ) vs. wavelength from U to 1, probably due to Faraday rotation or due to fact that the polarized radiation seen in the different wavelength bands comes from different parts of the accretion region. The phase dependence of the position angle requires field and accretion geometry more complicated than a simple centered dipole and a second emitting region producing weaker intermediate pulses in the infrared seems to be present. We derive the value of the inclination of the system i = 55° ± 5° , the colatitude of the active pole βl = 38° ± 5° i and the second emitting region β2 = 115° ± 5° , both of which are nearly at the same longitude facing the main accretion stream.

Circular polarimetry in the red and simultaneous photometric observations in the UBVRI bands during the period June 1-3, 1981, are discussed. The peak value of negative circular polarization PV ~ -15 % is stronger than observed in 1976-79. Variations in the shape of the polarization and light curves occur from night to night. The positive crossover and reversal of the sign of the circular polarization are only marginal. A probable explanation of the short term variations seems to be the changing shape and position of the accretion columns with respect to the magnetic axis

Circular polarimetry in the red and simultaneous photometric observations in the UBVRI bands during the period June 1-3, 1981, are discussed. The peak value of negative circular polarization PV ∿ -15% is stronger than observed in 1976–79. Variations in the shape of the polarization and light curves occur from night to night. The positive crossover and reversal of the sign of the circular polarization are only marginal. A probable explanation of the short term variations seems to be the changing shape and position of the accretion columns with respect to the magnetic axis.

Commission 42 convened for two business meetings and two scientific sessions. In the following, the minutes of the business meetings and a summary of the scientific meetings are presented, with the abstracts of some of the papers read.

Variable linear polarization has been detected in CH Cyg. Observations in 1977–79 (UBV) and 1979–80 (UBVRI) are presented. The amount of polarisation increases towards ultraviolet and the observed values range from 0.34 to 1.85% in the ultraviolet, and 0.04 to 0.68% in the yellow light. In the red and infrared observations the polarizationwas typically less than 0.1 %. Daring the interval September 1977 – February 1978 and in May 1980 a second component of polarization, with different direction and wavelength dependence, was present, resulting in a strong rotation of the position angle as a function of wavelength. The R and I observations of May 1980 (PR ≅ 0.4 %, PI ≅ 0.5%) showed that the second component was increasing towards the infrared. The peculiar wavelength dependence of polarization and position angle could be explained by variations in particle size and scattering geometry in a complicated dust envelope around the M giant. Another hypothesis is that the component of polarization increasing towards the ultraviolet is produced by electron scattering in an extended envelope of a hot companion and the second component by transient dust envelope of the M giant.

The BL Lac-type object OJ287, with a redshift z = 0.306 and a luminosity exceeding 1047 erg s−1 at maximum light, is among the brightest and most violently variable objects of its class. Rapid variations, with timescales of a few hours or less, have been reported over a wide range of wavelengths1,2 and also in polarization3, imposing strong constraints on the size and dynamics of the source4,5. The detection of periodic variations in OJ287, or in any other compact extragalactic source, would be even more important, as these could be related to rotation or orbital motion in the source. So far the only searches sensitive to periodic variations shorter than 1 h are the photometric observations of Visvanathan and Elliot6, Frohlich et al.7 and Kiplinger8, in which a 40-min period in OJ287 was respectively found, confirmed and not detected. We report here the detection of a 15.7-min periodic flux variation in OJ287 in April 1981 at 37 GHz. The source has been subsequently monitored for 265 h at 22 and 37 GHz, as well as in optical photometry, and the same period has been seen in simultaneous observations. The peak–peak amplitude of the variation is 1–10% of the total intensity. Other periods may also exist.

The undisturbed eclipse timings of U Cep obtained over the last decade are discussed. It is shown that abrupt period changes of both signs were separated by intervals of essentially constant period. The apparent lack of a gradually changing period rules out a steadily-acting tidal torque in the Biermann-Hall (1973) theory. The most recent period decrease (April 1979) occurred rapidly (less than 40 days) and left no visible trace of circumstellar matter. Possible mechanisms of period changes of both signs are examined.

Simultaneous radio, visual, and ultraviolet observations of the RS Canum Venaticorum binaries UX Arietis and HR 1099 are reported. The joint program covered the interval 1976 September 22 through October 3. The observations consisted of radio flux density measurements at 1660, 2695, and 8085 MHz; uv spectrophotometry of L..cap alpha.. and Mg II h and k; H..cap alpha.. and Ca II H and K spectroscopy; V-band photometry; and UBV polarimetry. A quasi-sinusoidal variation in V was observed in both systems. The period of this variation was approximately equal to the orbital period. No significant optical polarization was observed from either system. Variable radio emission was detected from both binaries throughout the program. Variable H..cap alpha.. and L..cap alpha.. emission were observed from HR 1099. UX Ari also exhibited L..cap alpha.. emission. Multiple Mg II emission components with peculiar velocities up to 250 km s/sup -1/ were often seen from both systems. Each Mg II observation also exhibited a strong and variable central velocity component which always seemed to match the orbital velocity of the more massive star in each system. HR 1099 exhibited strong Ca II H and K emission which was not significantly variable. The joint observations provide strongmore » evidence for chromospheric activity associated with the more massive star in each binary. Although the radio emission is produced in a larger volume than the optical and uv activity, temporal correlations suggest that a physical connection may exist between the two phenomena. 14 figures, 2 tables.« less