Ob-Stars on the utmost Borders of M 31

In a field of 4 square degrees, including the southwestern part of M 31 18 blue starlike objects are found by a photometric statistics in U,B,V of all starlike objects in this field. With great probability 13 of them are OB stars of M 31. Their utmost distances from the nucleus of M 31 are 35…50 kpc. Three further objects are probably quasistellar objects. Two others are striking by their extraordinary position in the two-colour diagram and cannot be classified in a distinct category of objects.     

Suspected OB stars near the andromeda nebula

An investigation of suspected OB stars on plates of the Schmidt telescope of Karl Schwarzschild Observatory Tautenburg gave the following results: I. There exists a sharp boundary of the M 31 disk. For distances larger than R = 30 kpc from the centre no OB stars of the Andromeda galaxy could be found. 2. The isolated OB stars in the outer regions of M 31 fit into the spiral structure. 3. The suspected OB stars outside M 31 (R>30 kpc) in all probability belong to our own galaxy. It is to be expected that they partly are blue horizontal branch stars of extreme population II, partly white dwarfs rather far left of the black body line in the two colour diagram.     

Search for optical identifications in the 5C3-radio survey I. Observations

In this paper the search for optical identifications in the 5C-radio surveys is continued. Near the positions of 135 radio sources of the 5C3 catalogue all present optical objects up to the plate limit (about B ≈︁ 21) have been measured photometrically in UBVr and astrometrically on plates of the 134/200 cm Schmidt telescope of the Karl Schwarzschild Observatory Tautenburg. A total of 111 candidates for possible optical identifications were found. The number of real identifications will be, of course, much smaller. Among the 111 objects there are: 12 supposed QSO's, 21 galaxies or probable galaxies, 56 stellar objects the greater part of which may be main sequence stars, subdwarfs and white dwarfs, and I object may be the centre of an H II region in the OB-association OB 182. 21 objects near the plate limit could not be classified. A statistical treatment with information on the real rate of identification (it roughly will amount to about 10%) and its reliability will be given in part III.     

Search for New Interesting Objects in the Second Part of the FBS

We present the results of a study of the FBS blue stellar objects with the goal of discovering new interesting objects. Forty-seven FBS objects have been observed with the Byurakan Observatory 2.6m telescope in 1987-1991 and scanned with the MAMA scanning machine at Observatoire de Paris in 1997-1999. 5 QSOs/Sy1s, 4 emission-line stars, five white dwarfs, and a number of continuous spectra objects (possible BL Lacs and DC white dwarfs) have been revealed.     

New faint optical spectrophotometric standards: hot white dwarfs from the Sloan Digital Sky Survey

The spectral energy distributions for pure-hydrogen (DA) hot white dwarfs can be accurately predicted by model atmospheres. This makes it possible to define spectrophotometric calibrators by scaling the theoretical spectral shapes with broad-band photometric observations – a strategy successfully exploited for the spectrographs onboard the Hubble Space Telescope ( HST ) using three primary DA standards. Absolute fluxes for non-DA secondary standards, introduced to increase the density of calibrators in the sky, need to be referred to the primary standards, but a far better solution would be to employ a network of DA stars scattered throughout the sky. We search for blue objects in the sixth data release of the Sloan Digital Sky Survey (SDSS) and fit DA model fluxes to identify suitable candidates. Reddening needs to be considered in the analysis of many of these stars. We propose a list of nine pure-hydrogen white dwarfs with absolute fluxes with estimated uncertainties below 3 per cent, including four objects with estimated errors <2 per cent, as candidates for spectrophotometric standards in the range  14 < g < 18  , and provide model-based fluxes scaled to match the SDSS broad-band fluxes for each. We apply the same method to the three HST DA standards, linking the zero point of their absolute fluxes to ugr magnitudes transformed from photometry obtained with the US Naval Observatory 1-m telescope. For these stars, we estimate uncertainties of <1 per cent in the optical, finding good consistency with the fluxes adopted for HST calibration.     

New ultracool and halo white dwarf candidates in SDSS Stripe 82

A     region along the celestial equator (Stripe 82) has been imaged repeatedly from 1998 to 2005 by the Sloan Digital Sky Survey (SDSS). A new catalogue of ∼4 million light-motion curves, together with over 200 derived statistical quantities, for objects in Stripe 82 brighter than   r ∼21.5  has been constructed by combining these data by Bramich et al. This catalogue is at present the deepest catalogue of its kind. Extracting ∼130 000 objects with highest signal-to-noise ratio proper motions, we build a reduced proper motion diagram to illustrate the scientific promise of the catalogue. In this diagram, disc and halo subdwarfs are well-separated from the cool white dwarf sequence. Our sample of 1049 cool white dwarf candidates includes at least eight and possibly 21 new ultracool H-rich white dwarfs  ( T _eff < 4000 K)  and one new ultracool He-rich white dwarf candidate identified from their SDSS optical and UKIDSS infrared photometry. At least 10 new halo white dwarfs are also identified from their kinematics.     

New Dwarf Galaxies in the M81/M82 Group

A survey for dwarf galaxies (Sculptor-type dwarfs) was carried out in the M81/M82 group of galaxies in an area of about 195 sq. degrees by means of Tautenburg 52-in. Schmidt plates. Eight new faint dwarf galaxies were discovered. Coordinates, linear and absolute dimensions as well as finding charts are given. Results of the photometry will be published in a second article.     

A search for nearby counterparts to the moving objects in the Hubble Deep Field

Ibata et al. have recently discovered very faint, moving objects in the Hubble Deep Field (HDF). The number, apparent magnitudes and proper motions of these objects are consistent with old white dwarfs making up part of the Galactic dark halo. We review a number of ground-based proper motion surveys in which nearby dark-halo white dwarfs might be present, if they have the colours and absolute magnitudes proposed. No such objects have been found, whereas we argue here that several times more would be expected than in the HDF. We conclude that it is unlikely that hydrogen-atmosphere white dwarfs make up a significant fraction of the Galactic dark matter. No limits can be placed as yet on helium-atmosphere dwarfs from optical searches.     

Structural investigations in the central part of the coma cluster on the base of equidensity diagrams. II

On the base of Tautenburg UBV-Schmidt plates equidensitometric diameters of galaxies of ROOD and BAUM 's list are given and the ellipticities in the three colours are determined. It was found that there is no difference in the ellipticities depending on the colours, on the average. The percentage of spherical objects (ε = 0.00) was found to 21.5 per cent. The surface brightness for 213 objects in the system V is given. The mean surface brightness is 22.75 mag/□′ with a dispersion of 2.5 mag/□′. It shows only a very slight dependence on the integrated magnitude.     

A new magnetic white dwarf: PG 2329+267

We have discovered that the white dwarf PG 2329+267 is magnetic, and, assuming a centred dipole structure, has a dipole magnetic field strength of approximately 2.3 MG. This makes it one of only approximately 4 per cent of isolated white dwarfs with a detectable magnetic field. Linear Zeeman splitting, as well as quadratic Zeeman shifts, is evident in the hydrogen Balmer sequence and circular spectropolarimetry reveals ∼10 per cent circular polarization in the two displaced σ components of Hα. We suggest from comparison with spectra of white dwarfs of known mass that PG 2329+267 is more massive than typical isolated white dwarfs, in agreement with the hypothesis that magnetic white dwarfs evolve from magnetic chemically peculiar Ap and Bp type main-sequence stars.     

Absolute proper motions of blue objects in the vicinity of M33

36 objects with mainly negative (U—B) indices were investigated for variability and proper motions. 10 objects with significant or suspected proper motions and 8 variable objects were detected. Using these criteria, it was possible to separate white dwarfs from quasi-stellar objects to some extent.     

The fraction of double degenerates among DA white dwarfs

We present the results of a radial velocity survey designed to measure the fraction of double degenerates among DA white dwarfs. The narrow core of the H line was observed twice or more for 46 white dwarfs yielding radial velocities accurate to a few km s¹. This makes our survey the most sensitive to the detection of double degenerates undertaken to date. We found no new double degenerates in our sample, though H emission from distant companions is seen in two systems. Two stars known to be double degenerates prior to our observations are included in the analysis. We find a 95 per cent probability that the fraction of double degenerates among DA white dwarfs lies in the range [0.017, 0.19].     

Herbig-Haro objects—tracers of the formation of low-mass stars and sub-stellar objects

Herbig-Haro objects (HHOs) are caused by outflows from young objects. Since the outflow relies on mass accretion from a circumstellar disk, it indicates ongoing growth. Recent results of infrared observations yielded evidence for disks around brown dwarfs. This suggests that at least a certain fraction of brown dwarfs forms like stars. Thus, young sub-stellar objects might cause HHOs as well. We present selected results of a general survey for HHOs based on DSS-II plates and CCD images taken with the Tautenburg Schmidt telescope. Numerous young objects could be identified due to their association with newly detected HHOs. In some cases the luminosity is consistent with very low-mass stars or close to sub-stellar values. This holds for L1415-IRS and a few infrared sources embedded in other dark clouds (e.g., GF9, BHR111). The question on the minimum mass for outflow activity is addressed.     

On the variability of the “blue objects”

The reality of the high percentage of variability among Blue Objects which was found in previous investigations was examined on 170 Tautenburg Schmidt plates of two test fields near M 31. The high percentage could not be confirmed. Spurious amplitudes can be explained by the large probable errors of the photometry (especially near the plate limit) and by bad suitability of good-looking plates. Out of 37 Blue Objects examined, only two (van den Bergh 5 and 12) are distinctly variable, but the final examination of Blue Objects which are suspected of variability can only be done by photoelectric photometry.     

An optical spectroscopic HR diagram for low-mass stars and brown dwarfs in Orion

The masses and temperatures of young low-mass stars and brown dwarfs in star-forming regions are not yet well established because of uncertainties in the age of individual objects and the spectral type–temperature scale appropriate for objects with ages of only a few Myr. Using multi-object optical spectroscopy, 45 low-mass stars and brown dwarfs in the Trapezium Cluster in Orion have been classified and 44 of these confirmed as bona fide cluster members. The spectral types obtained have been converted to effective temperatures using a temperature scale intermediate between those of dwarfs and giants, which is suitable for young pre-main-sequence objects. The objects have been placed on a Hertzsprung–Russell (HR) diagram overlaid with theoretical isochrones. The low-mass stars and the higher mass substellar objects are found to be clustered around the 1 Myr isochrone, while many of the lower mass substellar objects are located well above this isochrone. An average age of 1 Myr is found for the majority of the objects. Assuming coevality of the sources and an average age of 1 Myr, the masses of the objects have been estimated and range from  0.018 to 0.44 M_⊙  . The spectra also allow an investigation of the surface gravity of the objects by measurement of the sodium doublet equivalent width. With one possible exception, all objects have low gravities, in line with young ages, and the Na indices for the Trapezium objects lie systematically below those of young stars and brown dwarfs in Chamaeleon, suggesting that the 820 nm Na index may provide a sensitive means of estimating ages in young clusters.     

First Observation of Objects Found by the Tautenburg Objective Prism Survey

The spectra of ten objects discovered by the Tautenburg objective prism survey were obtained at a higher spectral resolution in order to refine the selection criteria. We found four objects to be quasars and three MARKARIAN -type galaxies.     

The DODO survey – II. A Gemini direct imaging search for substellar and planetary mass companions around nearby equatorial and Northern hemisphere white dwarfs

The aim of the Degenerate Objects around Degenerate Objects (DODO) survey is to search for very low-mass brown dwarfs and extrasolar planets in wide orbits around white dwarfs via direct imaging. The direct detection of such companions would allow the spectroscopic investigation of objects with temperatures much lower  (<500 K)  than the coolest brown dwarfs currently observed. These ultra-low-mass substellar objects would have spectral types >T8.5, and so could belong to the proposed Y dwarf spectral sequence. The detection of a planet around a white dwarf would prove that such objects can survive the final stages of stellar evolution and place constraints on the frequency of planetary systems around their progenitors (with masses between 1.5 and 8   M_⊙  , i.e. early B to mid-F). This paper presents the results of a multi epoch J band common proper motion survey of 23 nearby equatorial and Northern hemisphere white dwarfs. We rule out the presence of any common proper motion companions, with limiting masses determined from the completeness limit of each observation, to 18 white dwarfs. For the remaining five targets, the motion of the white dwarf is not sufficiently separated from the non-moving background objects in each field. These targets require additional observations to conclusively rule out the presence of any common proper motion companions. From our completeness limits, we tentatively suggest that  ≲5 per cent  of white dwarfs have substellar companions with   T _eff≳ 500 K  between projected physical separations of 60–200 au.     

Selection,Statistics and Photometry of Compact Galaxies with Different Instrumental Equipment. Part I

On plates taken with 2 different photographic telescopes compact galaxies in 3 fields near M₃ and M₉₂ were selected. The integral magnitudes and maximum angular diameters of the compacts were determined. The RITCHEY -CHRéTIEN telescope of the FIGL Observatory for Astrophysics (FOA) with a focal ratio of 1:8.3 has a scale of 1 mm = 16.3, while the Tautenburg SCHMIDT with 1:3.2 has a scale of 1 mm ≌ 52°. From the selection statistics for both telescopes results nearly the same number of objects (50) up to 18^m.5 in V in a field of 1.5□°.60% of these objects are identical. An integral photometry on B plates of the same limiting magnitude from both telescopes leads to nearly the same brightness of objects, while they are o^m.5 fainter on FOA V plates. Because of its smaller focal ratio this telescope does not record the halo parts of the compacts. This is clearly demonstrated by the maximum equidensitometric diameters which on FAO plates are on the average only half of those determined on Tautenburg plates. A diameter magnitude diagram is shown.     

New stellar and substellar candidate members of the Coma Berenices open star cluster

We present the results of a survey of the open star cluster Melotte 111 in Coma Berenices, undertaken using the USNO‐B1.0 and 2MASS Point Source catalogues. On the basis of their astrometric and photometric properties, we have identified 60 new candidate members with masses in the range 1.007 < M < 0.269 M_⊙. We estimate a membership probability for each by extracting control clusters from the proper motion vector diagram. All 60 are found to have greater than 60 per cent probability of being cluster members, which if they are confirmed as members, more than doubles the number of known cluster members. We also have I and Z photometry for 100 low mass candidate members of the cluster, 13 of which we suggest may be brown dwarfs. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)