Further observations of the filamentary nebulosity around the cetus Arc (Loop 2)

Previously some filamentary nebulosity was discovered around the outer edge of the Cetus Arc (Loop 2). Some further observations have now been made of this. To determine an upper limit to its proper motion it was photographed again with the Mount Palomar 48-inch Schmidt telescope. Also, to reveal the full extent of this nebulous region, more photographs have been added to the original mosaic and it has been photographed again with a wider field filter camera. No proper motion greater than 0 _. 5/year was detected. However, some further ridges of nebulosity were discovered.A shell model for Loop 2 based on this upper limit to the proper motion of the nebulosity and its similarity to the Cygnus Loop is presented. Some comments on the excitation mechanism of the nebulosity are also made.     

Emission-line CCD imaging of three southern symbiotic stars

Symbiotic stars that are strong radio sources and have cool dust emitting in the infrared are expected to have extended emission nebulae around them. In order to search for such emission nebulae, we have carried out CCD imaging of three symbiotic stars (R Aqr, RR Tel and H1-36) with narrow-band filters centred at the emission lines of [O III] λ5007, Hα λ6563, [N II] λ6584, [S II] λ6717 + 6731. RR Tel and H1-36 images do not show any extended nebulosities around them. The CCD image of the R Aqr nebulosity in the high excitation [O m] line is different from its image in Hα and the low excitation lines of [N II] and [S II] indicating ionization-stratification in the nebula. In H1-36 the optical nebulosity (if it exists) is smaller than ∽2 arcsec while the radio image size is known to be large (∽5 arcsec). This behaviour is opposite to that seen in R Aqr in which the radio emission comes from the core region of a much larger optical nebulosity. Interstellar and/or circumstellar extinctions are suggested to be responsible for this difference     

Appearance of a nebula near Y Ori

The results of photographic and photoelectric observations for the star Y Ori are presented. During these observations a red nebulosity appeared around the star Y Ori near the maximum of brightness. The optical sizes of the nebulosity are comparable with the OH sizes of long period variables and OH/IR stars. A real brightness increase on the decreasing branch of the light curve was detected in U spectral band.Published in Astrofizika, Vol. 38, No. 4, pp. 555–558, October–December, 1995.     

S 235 B explained: an accreting Herbig Be star surrounded by reflection nebulosity

The intent of this study is to determine the nature of the star and associated nebulosity S 235 B, which are located in a region of active star formation still heavily obscured by the parent molecular cloud. Low-resolution  ( R = 400)  long-slit spectra of the star and nebulosity, and medium-  ( R = 1800)  and high-resolution  ( R = 60 000)  spectra of the central star are presented along with the results of Fabry–Perot interferometric imaging of the entire region. Based on the long-slit and Fabry–Perot observations, the nebulosity appears to be entirely reflective in nature, with the stellar component S 235 B★ providing most of the illuminating flux. The stellar source itself is classified here as a B1V star, with emission-line profiles indicative of an accretion disc. S 235 B★ thus belongs to the relatively rare class of early-type Hebrig Be stars. Based on the intensity of the reflected component, it is concluded that the accretion disc must be viewed nearly edge-on. Estimates of the accretion rate of S 235 B★ from the width of the Hα profile at 10 per cent of maximum intensity, a method which has been used lately for T Tauri stars and Brown Dwarfs, appear to be inconsistent with the mass outflow rate and accretion rate implied from previous infrared observations by Felli et al., suggesting this empirical law does not extend to higher masses.     

A reappraisal of several extensive phenomena of the high galactic latitudes

This is the first of two papers dealing with the extensive high latitude phenomena. The relationships between the diffuse and filamentary gaseous nebulosity, the giant radio loops and the high, medium and low velocity neutral hydrogen are considered in the light of recent observations. The existence of other giant loops is also suggested.A further article (by K.H.E.) will present some very accurate measurements of the radial velocities of the nebulosities in the vicinity of Loop 2. These will be compared to some neutral hydrogen features in that region.     

A model for a structure in the galactic nebula S206

The galactic nebula S206 contains a half shell of high excitation nebulosity which is centred on the associated exciting star. The suggestion has been made that this structure is caused by the interaction of stellar mass loss from the star with nebular gas. A steady state model of such an interaction is investigated quantitatively. The required mass loss rate from the star is about 10^–7 M yr^–1 which is compatible with the observationally derived mass-loss rates from early-type stars.     

Collaborative research of open star clusters

Preliminary results on observations of open clusters are presented. The project has been initiated in the framework of the Uzbek-Taiwan and Taiwan-Baltic collaboration, mainly to upgrade and make use of facilities at Maidanak Observatory. We present detailed, multiwavelength studies of the young cluster NGC 6823 and the associated complex nebulosity, to diagnose the young stellar population and star formation history in the region. In addition, 7 compact open clusters have been monitored for stellar variability. We show how observations like these could feasibly be used to look for exoplanet transit events. We also expect to join the Whole-Earth Telescope effort in future campaigns for asteroseismology.     

Direct observations of bipolar outflow from HM sagittae

We observed HM Sagittae with theMulti-Element Radio Linked Interferometer Network (MERLIN) at 6 cm and 18cm. We find non-thermal bipolar outflow in the eastwest direction, associated with optical emission lines, and thermal ridges to the north and south associated with the UV nebulosity detected by the HST.     

The nearest stellar wind bubble or fossil supernova remnant

A new series of ultra-deep, wide-angle H filter photographs at higher angular resolution than hitherto achieved, have been obtained covering the Orion-Taurus-Eridanus region. These reveal new, both diffuse and filamentary nebulosities near the Barnard Arc Nebula, which are correlated with Hi features in the region. Mechanisms capable of producing the observed features are discussed. Both a stellar wind bubble and a fossil supernova remnant are considered possible explanations, and would represent the nearest examples of these features to the Sun. Furthermore, nebulosity in this region has been photographed for the first time at [Nii]. The possible implications of this and other observations are discussed.     

Infrared photometry,extinctions andR values for some Northern Milky Way stars

Infrared wideband photometry for 21 early-type stars in the Northern Milky Way is used to determine extinction values by the colour-difference method. The mean extinction curve is similar to the van de Hulst theoretical curve No. 15, and there is no significant difference in the results for stars lying towards and away from nebulosity. None of the stars exhibit infrared excesses at 3.5 . A mean value ofR=3.15±0.15 is deduced for the ratio of total to selective extinction.R is found to be normal towards the open cluster IC 1805 for which high values have been suggested; a distance of 2.0±0.2 kpc is deduced for this cluster.Visiting astronomer, Kitt Peak National Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Quasi-stellar objects and evolution of galaxies

In view of the striking similarities between Quasi-Stellar Objects on the one hand and the nuclei of N galaxies, Seyfert galaxies, radio galaxies and normal galaxies on the other, the possibility that QSOs might belong to an early phase in the evolutionary sequence of galaxies is explored. In this connection, considering the fact that nebulosities have been detected around five QSOs, the implications of the hypothesis that a QSO consists of a bright central object embedded in an extended nebulosity have been examined. In particular, the ratio a between the intensity of the bright central object and that of the surrounding nebulosity in the visual band of wavelengths has been calculated by the colour-given method for a sample of 81 QSOs with emission redshiftz0.76. This ratio a has been used to calculate the apparent visual magnitudem(V) and the absolute visual magnitudeM(V) of the bright central object (Nu) as well as that of the surounding nebulosity (Neb) of the QSOs in the sample and a criterion has been proposed as to the detectability of the surrounding nebulosities. Similar calculations have been made for N galaxies, Seyfert galaxies and normal galaxies. It is found that the values of log a, M(V) _Nu and M(V) _Neb for the four classes of extragalactic objects show a definite trend and suggest an evolutionary sequence: QSOsN galaxiesSeyfert galaxiesnormal galaxies.     

Deep Hα imagery of the Eridanus shells

A deep Hα image of interlocking filamentary arcs of nebulosity has been obtained with a wide-field (≈30° diameter) narrow-band filter camera combined with a charge-coupled device as a detector. The resultant mosaic of images, extending to a galactic latitude of −65°, has been corrected for field distortions and had galactic coordinates superimposed on it to permit accurate correlations with the most recent H  i (21 cm), X-ray (0.75 keV) and FIR ( IRAS 100 μm) maps.
Furthermore, an upper limit of 0.13 arcsec yr⁻¹ to the expansion proper motion of the primary 25° long nebulous arc has been obtained by comparing a recent Hα image obtained with the San Pedro Martir telescope of its filamentary edge with that on a Palomar Observatory Sky Survey E plate obtained in 1951.
It is concluded that these filamentary arcs are the superimposed images of separate shells (driven by supernova explosions and/or stellar winds) rather than the edges of a single 'superbubble' stretching from Barnard's Arc (and the Orion Nebula) to these high galactic latitudes. The proper motion measurement argues against the primary Hα-emitting arc being associated with the giant radio loop (Loop 2) except in extraordinary circumstances.     

Photographic photometry for stellar statistics with Tautenburg Schmidt telescope

Photometric properties of deep Tautenburg Schmidt plates in the UBV system over the whole field and over a wide range of stellar magnitudes are discussed. Different reduction models based on the calibration curve alone and with additional terms containing colour and plate coordinates are considered. With the filter-emulsion combinations used the Johnson UBV system can be reproduced quite well by the Tautenburg telescope. The accuracy of photometric data can be improved if geometrical terms are taken into account. For deep plates with a significant effect of background nebulosity a supplementary term is to be included in the reduction model. The polynomial coefficients vary in dependence on spectral bands and individual properties of each plate.     

A Herbig–Haro object associated with GGD30 and its exciting source

GGD30 has been suggested to be either a small reflection nebulosity or a Herbig–Haro (HH) object formed in the outflow from a nearby obscured star. Observations to date have not been able to distinguish between these two scenarios. In addition, there are conflicting proposals for the location of the exciting source for GGD30. To resolve these questions, we have carried out optical spectroscopy and near-infrared ( J , K and 3.6-μm) imaging of GGD30. Taken together, these observations reveal that the bright optical knot in GGD30 must be a HH object, excited by the outflow from an optically obscured pre-main-sequence (PMS) star located ∼3 arcsec to the southwest. Based on mid-infrared fluxes from the Mid-course Space Experiment ( MSX ) satellite, we estimate the luminosity of this PMS star to be  ∼12.5 L_⊙  which suggests it is an intermediate-mass object rather than low-mass as previously proposed. The optical spectroscopy indicates projected velocities of  ∼−270 km s⁻¹  associated with the HH object. The fact that these velocities are blueshifted and relatively high compared to the velocities typical of HH flows suggests that the outflow from the PMS star must be almost aligned with the line of sight. There is an additional low-velocity  (∼−70 km s⁻¹) Hα  component but its origin is not clear.     

The unusual supernova remnant surrounding the ultraluminous X-ray source IC 342 X-1

We report the results of an observation of a large-diameter (110 pc) supernova remnant (SNR) found to encircle the position of the ultraluminous X-ray source (ULX) IC 342 X-1. The inferred initial energy input to the SNR is at least 2–3 times greater than the canonical energy for an 'ordinary' SNR. Two regions on the inside of the shell are bright in [O iii ]λ5007 emission, possibly as the result of X-ray photoionization by the ULX. If this is the case, then the morphology of this nebulosity implies that the X-ray emission from the ULX is anisotropic. The presence of the ULX, most probably a black hole X-ray binary, within an unusually energetic SNR suggests that we may be observing the aftermath of a gamma-ray burst, although other origins for the energetic nebula are discussed.     

On the distance to the Ophiuchus star‐forming region

The Ophiuchus molecular cloud complex has produced in Lynds 1688 the richest known embedded cluster within ∼300 pc of the Sun. Unfortunately, distance estimates to the Oph complex vary by nearly ∼40% (∼120–165 pc). Here I calculate a new independent distance estimate of 135±8 pc to this benchmark star‐forming region based on Hipparcos trigonometric parallaxes to stars illuminating reflection nebulosity in close proximity to Lynds 1688. Combining this value with recent distance estimates from reddening studies suggests a consensus distance of 139±6 pc (4% error), situating it within ∼11 pc of the centroid of the ∼5 Myr old Upper Sco OB subgroup of Sco OB2 (145 pc). The velocity vectors for Oph and Upper Sco are statistically indistinguishable within ∼1 km s^–1 in each vector component. Both Oph and Upper Sco have negligible motion (<1 km s^–1) in the Galactic vertical direction with respect to the Local Standard of Rest, which is inconsistent with the young stellar groups having formed via the high velocity cloud impact scenario. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Southern YSO GRV10 and its environment

In this paper the southern cometary nebula GRV10 and its environment are investigated. The object is connected with a molecular cloud (its dimensions are ~4 pc). 12CO (1-0) observations toward GRV10 revealed the presence of two molecular outflows (a bipolar outflow), a red and a blue-shifted outflow, which coincide in position, indicating that they are moving along the line of sight in opposite directions. Near GRV10 a bright IR star, GRV10 IR, is discovered (near the southern edge of the nebula) and since its spectra and near IR colors favor it to be a Mira type star, a distance of ~4.4 kpc can be estimated. Star GRV10 IR appears connected with the IRAS point source IRAS 10406-6256. The grouping of stars (YSOs - young stellar objects) connected with GRV10 and embedded in a dark nebulosity is also discussed. This grouping is associated with the IRAS point source IRAS 10406-6253, which has FIR colors typical for embedded, not evolved, YSOs.     

The structure of the Cygnus loop at 34.5 MHz

We have observed the large supernova remnant Cygnus Loop at 34.5 MHz with the low frequency radio telescope at Gauribi-danur, India. A radio map of the region with a resolution of 26 arcmin × 40 arcmin (α × δ) is presented. The integrated flux density of the Cygnus Loop at this frequency is 1245 ± 195 Jy. The radio fluxes of different parts of the nebula at this frequency were also measured and used to construct their spectra. It is found that the spectrum of the region associated with the optical nebulosity NGC 6992/5 is not flat at low frequencies, and also exhibits a break at a frequency around 400 MHz. The spectrum of the region associated with NGC 6960 also shows a break but around 1000 MHz, while the spectrum of the region associated with NGC 6974 is straight in the entire frequency range 25 to 5000 MHz. The implication of these results on the basis of existing theories of the origin of radio emission from supernova remnants is discussed.     

Multicolor photoelectric and photographic observations of the long-period variable Y Ori

Results of observations of the long-period variable Y Ori are presented. The photoelectric observations in UBVR were made at the 60-cm telescope of the high-altitude Maydanak station of the Tashkent Astronomical Institute during the autumn of 1989. The UBVR lightcurves as well as the variations in the color indices U-B, B-V, and V-R are presented. The photographic observations were made at the 40 Schmidt telescope of the Byurakan Observatory and at the 70-cm Maksutov telescope of the Abastumani Observatory. A nebulosity was discovered around Y Ori in red light near the brightness maximum. Such a formation is observed for the first time, not only for Y Ori but also for long-period variables in general. The obtained results are discussed in this work.Translated fromAstrofizika, Vol. 38, No. 1, pp. 5–15, January–March, 1995.