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The initial conditions of isolated star formation - IX. Akari mapping of an externally heated pre-stellar core
We present observations of L1155 and L1148 in the Cepheus molecularcloud, taken using the Far Infrared Surveyor (FIS) instrument on theAkari satellite. We compare these data to submillimetre data taken usingthe Submillimetre Common-User Bolometer Array (SCUBA) camera on theJames Clerk Maxwell Telescope, and far-infrared data taken with theimaging photo-polarimeter (ISOPHOT) camera on board the Infrared SpaceObservatory (ISO) satellite. The Akari data cover a similar spectralwindow and are consistent with the ISO data. All of the data show arelation between the position of the peak of emission and the wavelengthfor the core of L1155. We interpret this as a temperature gradient. Wefit modified blackbody curves to the spectral energy distributions attwo positions in the core and see that the central core in L1155(L1155C) is approximately 2° warmer at one edge than it is in thecentre. We consider a number of possible heating sources and concludethat the A6V star BD+67 1263 is the most likely candidate. This star isat a distance of 0.7pc from the front of L1155C in the plane of the sky.We carry out radiative transfer modelling of the L1155C core includingthe effects from the nearby star. We find that we can generate a goodfit to the observed data at all wavelengths, and demonstrate that thedifferent morphologies of the core at different wavelengths can beexplained by the observed 2° temperature gradient. The L1148 coreexhibits a similar morphology to that of L1155C, and the data are alsoconsistent with a temperature gradient across the core. In this case,the most likely heating source is the star BD197053. Our findingsillustrate very clearly that the apparent observed morphology of apre-stellar core can be highly dependent on the wavelength of theobservation, and that temperature gradients must be taken into accountbefore converting images into column density distributions. This isimportant to note when interpreting Akari and Spitzer data and will alsobe significant for Herschel data.
| Multicolour CCD measurements of visual double and multiple stars. III
Context: Recent CCD observations were performed in the period 1998-2004for a large sample of visual double and multiple stars selected from theHipparcos Catalogue and/or from the Gliese Catalogue of Nearby Stars. Aims: Accurate astrometric and photometric data allowing us tocharacterise the individual components are provided. These data arecompared to Hipparcos data or to data from an older epoch to assess thenature of the observed systems. Methods: We simultaneously apply aMoffat-Lorentz profile with a similar shape to all detected componentsand adjust the profile parameters from which we obtain the relativeastrometric position (epoch, position angle, angular separation) as wellas differential multi-colour photometry (filters (B)VRI). Results: Wethus acquired recent data for 71 visual systems of which 6 are orbitalbinaries, 27 are nearby, and 30 are multiple systems. In three of thesecases, the systems remained unresolved. 23 new components were detectedand measured. Two new visual double stars of intermediate separationwere also found. The estimated accuracies in relative position are0.04° and 0.01 arcsec respectively, while those in differentialphotometry are of the order of 0.01-0.02 mag in general. Conclusions:.The nature of the association of 55 systems is evaluated. New basicbinary properties are derived for 20 bound systems. Component coloursand masses are provided for two orbital binaries.Based on observations collected at the National AstronomicalObservatory, Rozhen, and the Astronomical Observatory, Belogradchik,both operated by the Institute of Astronomy, Bulgarian Academy ofSciences. Also based on data obtained by the Hipparcos astrometrysatellite. Appendix A is only available in electronic form athttp://www.aanda.org Tables 4-6 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/464/641
| On the distance of dark clouds in the vicinity of the reflection nebula NGC 7023 in Cepheus
Distance to a group of dark clouds at moderate galactic latitudes Lynds1147, 1148, 1152, 1155, 1157, 1158, 1167, 1168, 1170, 1171, 1172, 1173,and 1174 is estimated from the extinction AV vs distance plot. Thisdependence is based on photometry of 79 stars down to V = 12.5 in theVilnius photometric system and their two-dimensional classification. Thedistance of the L1147/1158 group of clouds is found to be 325 +/- 13 pcand that of the L1167/1174 or NGC 7023 group of clouds is 288 +/- 25 pc.A number of stars with peculiar energy distribution has been found.
| Interstellar extinction and polarimetric properties of the star HD 200775
Reddening and polarization are obtained and separated into intrinsic andinterstellar components for the Herbig Be star HD 200775, which issurrounded by the NGC 7023 reflection nebula. A reddening map based onstar counts is used to derive the relation between (C-13)O columndensity and extinction, and the maximum interstellar polarization isfound to be 0.88 percent at the maximum wavelength of 0.532 microns;this indicates that the size distribution of the particles in the cloudresponsible for the optical extinction and polarization is rathersimilar to that of the surrounding interstellar medium.
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Observation and Astrometry data
| Constellation: | Cepheus |
| Right ascension: | 20h46m32.32s |
| Declination: | +67°16'32.4" |
| Apparent magnitude: | 8.173 |
| Distance: | 344.828 parsecs |
| Proper motion RA: | -10.9 |
| Proper motion Dec: | -16.6 |
| B-T magnitude: | 8.475 |
| V-T magnitude: | 8.198 |
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