F. Mavromatakis

Discovery of the optical counterpart to the X-ray pulsar SAX J2103.5+4545

We report optical and infrared photometric and spectroscopic observations that identify the counterpart to the 358.6-s X-ray transient pulsar SAX J2103.5+4545 with a moderately reddened V = 14.2 B0Ve star. This identification makes SAX J2103.5+4545 the Be/X-ray binary with the shortest orbital period known, Porb = 12.7 days. The amount of absorption to the system has been estimated to be AV = 4.2 ± 0.3, which for such an early-type star implies a distance of about 6.5 kpc. The optical spectra reveal major and rapid changes in the strength and shape of the Hα line. The Hα line was ini- tially observed as a double peak profile with the ratio of the intensities of the blue over the red peak greater than one (V/R > 1). Two weeks later this ratio reversed (V/R < 1). Subsequently, in less than a month, the emission ceased and Hα appeared in absorption. This fast spectral variability is interpreted within the viscous decretion disc model and demonstrates the significant role of the neutron star on the evolution of the circumstellar disc around the Be star. The implications of the small orbit and moderate eccentricity on the spin period of the neutron star are discussed.

New planetary nebulae in the Galactic bulge region with l > 0°– I. Discovery method and first results

We present the first results of an [0 III] 5007 A interference filter survey for planetary nebulae (PNe) in the Galactic bulge. Covering (at first) the 66 per cent of the survey area, we detected a total of 90 objects, including 25 new PNe, 57 known PNe and eight known PNe candidates. Deep Hα+[N II] CCD images have been obtained as well as low-resolution spectra for the newly discovered PNe. Their spectral signature suggests that the detected emission originates from a photoionized nebula. In addition, absolute line fluxes have been measured and the electron densities are given. Accurate optical positions and optical diameters have also been determined.

Deep optical observations of G 65.3+5.7

We present the rst CCD mosaic of the supernova remnant G 65.3+5.7 in the optical emission lines of (O ii )a nd (Oiii). The new images reveal several diuse and lamentary structures both inside and outside the extent of the remnant as dened by its X{ray and radio emission. The medium ionization line of (O iii)5007 A provides the sharpest view to the system, while the remnant appears less lamentary in the emission line of (O ii). There are signicant morphological dierences between the two images strongly suggesting the presence of incomplete shock structures. Deep long{slit spectra were taken at several dierent positions of G 65.3+5.7. All spectra originate from shock heated gas, while the majority of them is characterized by large (O iii)/H ratios. The sulfur line ratios indicate electron densities below200 cm 3 , while estimates of the shock velocities lie in the range of 90{140 km s 1 . Finally, the observed variations of the H/H ratios may reflect the presence of

The supernova remnants G 67.7+1.8, G 31.5-0.6 and G 49.2-0.7

Wide field CCD observations of three, less known, supernova remnants. Filamentary and diffuse emission is discovered from the supernova remnant G67.7+1.8. Emission can also be seen in the ROSAT All Sky Survey data which indicate an extended hard X-ray source. The optical radiation from the G31.5-0.6 area shows weak sulfur emission and is probably not related to the remnant. Weak sulfur emission is also observed from W51C or G49.2-0.7. However, a small patch of emission in the south-east seems to emit strong sulfur emission. Results from long slit spectra are also presented.

Multi-wavelength study of the G 82.2+5.3 supernova remnant

We present the first CCD flux-calibrated images of the supernova remnant G 82.2+5.3 in major optical emission lines. The medium ionization line of (Oiii)5007 A provides the first direct evidence of optical emission originating from G 82.2+5.3. Filamentary emission is detected in the west and east areas of the remnant, roughly defining an ellipsoidal shell. The (Oiii) emission is rather well correlated with the radio emission suggesting their association, while typical fluxes are found in the range of 20-30 10 17 erg s 1 cm 2 arcsec 2 . Deep long-slit spectra taken at specific positions of the remnant verify that the detected filamentary emission originates from shock heated gas, while the diuse (Oiii) emission in the south results from photoionization processes. The spectra further suggest shock velocities around 100 km s 1 and low electron densities. The X-ray surface brightness is quite patchy, missing obvious limb brightening and is dominated by a bright bar-like emission region which is o-set from the geometric center by9 0 . The X-ray emission is thermal and requires two temperatures of 0.2 keV and 0.63 keV. The bright bar region shows overabundant Mg, Si and Fe, which might indicate still radiating ejecta matter. The azimuthally averaged radial surface profile is consistent with the matter density changing with distance r from the center/e r=r0 with a characteristic angular length of 36 0 , or, alternatively, with an r 1=2 density profile. The matter inside the remnant is quite likely structured like a porous cloudy medium. The average matter density is0.04 d 0:5 1:6 with d1:6 the distance in units of 1.6 kpc. Because of the low density and the long cooling times involved the remnant is more likely to be in the adiabatic phase, which is consistent with the densities derived for the X-ray plasma and the optical line emission, but it is not excluded that is has reached the radiating phase. This, however, would imply a lower density, greater age and much larger distance, at the edge of the upper limits obtained from NH and E(B V).

The physical structure of the planetary nebula NGC 6781

The planetary nebula NGC 6781 was imaged in major optical emission lines. These lines allow us to construct maps of the projected, two dimensional Balmer decrement, electron density, electron temperature, ionization and abundance structure. The average electron density, determined from the (S ii) lines, is500 cm 3 , while the electron temperature distribution, determined from the (N ii) lines, is flat at 10 000 K. The Balmer decrement map shows that there are variations in extinction between the north and south areas of the planetary nebula. The higher extinction observed to the north of the central star is probably caused by dust spatially associated with CO emission at blue{shifted velocities. The (N ii) image reveals the known optical halo, at a flux level of0.2% of the strong shell emission in the east, but now the angular extent of 216 00 190 00 is much larger than previous measurements. The halo is also present in (O iii), where we measure an extent of 190 00 162 00 .T he ionization maps indicate substantial ionization along the caps of the ellipsoid as well as in the halo. The maps also show a sharp decrease in ionization along the outer edge of the shell in the west and the east, south{east. The typical log abundances measured for He, N, O and S are 10.97, 8.14, 8.72 and 6.90, respectively.

Imaging and spectroscopy of the faint remnant G 114.3+0.3

We present the first calibrated CCD images of the faint supernova remnant G 114.3+0.3 in the emission lines of [OII], [OIII], Halpha+[NII] and [SII]. The deep low ionization CCD images reveal diffuse emission in the south and central areas of the remnant. These are correlated with areas of intense radio emission, while estimates of the [SII]/Halpha ratio suggest that the detected emission originates from shock heated gas. In the medium ionization image of [OIII] we discovered a thin filament in the south matching very well the outer radio contours. This filament is not continuous over its total extent but shows variations in the intensity, mainly in the south-west suggesting inhomogeneous interstellar clouds. Deep long-slit spectra were also taken along the [OIII] filament clearly identifying the observed emission as emission from shock heated gas. The Halpha emission is a few times 10^(-17) erg s^(-1) cm^(-2) arcsec^(-2), while the variations seen in the [OIII] flux suggest shock velocities into the interstellar clouds around or below 100 km/s. The sulfur line ratio approaches the low density limit implying electron densities less than ~500 cm^(-3).

The peculiar supernova remnant CTB 80

Deep CCD exposures of the peculiar supernova remnant CTB 80 in the light of the H +( Nii), (S ii), (O ii), and (O iii) lters have been obtained. These images reveal signicant shock heated emission in the area of the remnant. An extended bright diuse nebula in the south{east part of CTB 80 overlaps soft X-ray emission from ROSAT but it does not appear to be related to the remnant under study. New diuse and lamentary structures are detected to the south, south{east, and north of PSR 1951+32, most likely associated with CTB 80. Especially, the sulfur line image shows emission in the north along the outer boundary of the IRAS and HI shells. The (O iii) emission is lamentary, suggesting shock velocities greater than 100 km s 1 but its spatial extent is quite limited. Lower shock velocities are expected in the north and north{east areas of the remnant, since (O ii) emission is present, while (O iii) line emission is not detected. The comparison between the (O iii )a nd (Oii) line images further suggest the presence of signicant inhomogeneities in the interstellar medium. The flux{calibrated images do not indicate the presence of incomplete recombination zones, and we estimate that the densities of the preshock clouds should not exceed a few atoms per cm 3 . The typical projected angular widths of the observed laments are30 00 . Typical surface brightness values of the long (O iii) lament in the south are12 10 17 erg s 1 cm 2 arcsec 2 while the (O ii) image is characterized by fluxes of 10{20 10 17 erg s 1 cm 2 arcsec 2 . The area covered by the optical radiation along with the radio emission at 1410 MHz suggest that CTB 80 occupies a larger angular extent than was previously known.

The faint supernova remnant G 34.7-0.4 (W44)

Flux calibrated images of the known supernova remnant G 34.7-0.4 in basic optical emission lines are pre- sented. The low ionization images show a relatively flat flux distribution. The di use and patchy morphology of the de- tected optical emission may indicate the presence of turbulent magnetic fields. Typical observed H+ (Nii) fluxes are 8 10 17 erg s 1 cm 2 arcsec 2 , while the (Sii) fluxes are lower around 4 10 17 erg s 1 cm 2 arcsec 2 . Emission in the medium ionization line of (Oiii) 5007 A is not detected within our sensitivity limits, probably due to the heavy extinction towards the remnant. The long-slit spectra reveal strong (S ii )a nd (Nii) emission relative to H and moderate (Oi) 6300 A emission. Shock velocities in the range of 110-150 km s 1 and low electron densities are estimated. Archival MSX infrared data show emission in the south and west areas of the remnant matching rather well the optical and radio emission.

New optical filamentary structures in Pegasus

Deep Hα+(N ) CCD images have been obtained in the area of the Pegasus Constellation. The resulting mosaic covers an extent of ∼7. ◦ 5 × 8. ◦ 5 and filamentary and diffuse emission was discovered. Several long filaments (up to ∼1 ◦ )a re found within the field, while diffuse emission is present mainly in the central and northern areas. The filaments show variations in intensity along their extent suggesting inhomogeneous interstellar clouds. Faint soft X-ray emission was also detected in the ROSAT All-Sky Survey. It is mainly concentrated in the central areas of our field and overlaps the optical emission. The low ionization images of (S ) of selected areas mainly show faint diffuse emission, while in the medium ionization images of (O  )d iffuse and faint filamentary structures are present. Spectrophotometric observations were performed on the brightest filaments and indicate emission from photoionized or shock-heated gas. The sulfur line ratios indicate electron densities below ∼600 cm −3 , while the absolute Hα emission lies in the range of 1.1−8.8 ×10 −17 erg s −1 cm −2 arcsec −2 . The detected optical line emission could be part of a single or multiple supernova explosions.