Direct CCD Research Articles

ORBITAL PERIODS OF THE DWARF NOVAE AR AND, AM CAS, AND PY PER

ABSTRACT We present time-resolved spectroscopy of the dwarf-novae AR And, AM Cas, and PY Per. From velocities of H-alpha emission lines, we determine orbital periods of 0.16302 ± 0.00032 d (=3.91 h) for AR And and 0.15480 ± 0.00017 d (=3.72 h) for PY Per. Our period determination for AR And resolves a daily cycle-count ambiguity in a previous determination by Shafter, Veal, and Robinson (1995). No orbital period for PY Per has previously been published. The orbital period of Am Cas, determined here for hte first time, is constrained over a 46-night baseline to one of several precise values near 0.165 d (=3.96 h), the best of which are 0.16490 ± 0.00001 d and 0.16551 ± 0.0001 d. For PY Per, we use a single direct CCD exposure to extend the magnitude sequence of Misselt (1996). A comparison with the Downes & Shara atlas (1993) shows that PY Per had V ~ 19.8 when the Downes & Shara image was obtained, which is much fainter than the minimum listed in the General Catalogue of Variable Stars (Kholopov 1987). Our averaged spectra of all appear typical for dwarf novae, except that the Fe II lambda-5169 in AR And is unusally strong and weak features at lambda-5230, lambda-5270, and labmda-5322 (which we attribute to Fe II) also appear.

The Clover Leaf Quasar H1413+117: New Photometric Light Curves

Direct CCD images of the gravitationally lensed BAL quasar H1413+117 (Bessel B, V, R, I; Gunn r and i), obtained during 1989-1994 in the framework of photometric monitorings at ESO and with the NOT, have been carefully (re-)analyzed. Simultaneous fitting of 4 PSFs, fixing the relative positions of components B, C and D with respect to A, has been achieved successfully. The relative light curves of the 4 lensed QSO images, with respect to a stable nearby comparison star, confirm the general trend already presented by Arnould et al. (1993). The amplitude of the light curves is found to be about 0.5 magnitude, peak-to-peak in the V filter. The four lensed components display brightness variations quasi-simultaneously and in parallel. In addition to these intrinsic light variations due to the source, we find that component D shows extra light variations with respect to the other components. These are very likely caused by micro-lensing.

Ground-Based And HST Direct Imaging Of HLQs

In the context of our studies on gravitational lensing effects among Highly Luminous Quasars (HLQs), we are presently compiling at STScI an archive of direct CCD frames for more than 1000 bright quasars observed with HST and ground-based telescopes. This archive will soon become publicly accessible through the Internet. On the basis of these observations, we are pursuing in a systematic way the analysis (subtraction of numerical PSFs and/or deconvolution) of the HLQ images in order to detect multiple QSO images and/or nearby foreground galaxies at very small angular separations. Residual images corresponding to several new possible multiply imaged HLQs are presented here. From the observed number and image configuration of gravitational lens candidates identified in this large sample of HLQs, it is possible to infer realistic values for parameters characterizing the galaxy deflectors, the number counts of quasars, etc. (cf. Claeskens et al. 1995ab), and also to set interesting constraints on the cosmological density of compact objects in the mass range 1010 ‒ 1012M⊙.

FY Aquilae and the gamma-ray burst GB 790331

view Abstract Citations (4) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS FY Aquilae and the Gamma-Ray Burst GB 790331 Irwin, Mike ; Zytkow, Anna N. Abstract We have reexamined several classic gamma-ray bursts with relatively small error boxes and in this Letter we report on unusual optical phenomena in the vicinity of FY Aql, a Mira variable found inside the error box of GB 790331. We find no trace of the optical nebulosity seen surrounding FY Aql in 1986 observations, in either deep archival R-band photographic data from 1950 or in deep R-band CCD images taken in 1993. In addition, we have obtained detailed spectroscopy of the FY Aql system which reveals the presence of a significant 'blue bump' in the Mira spectrum. Model fitting of our direct CCD images confirms that FY Aql might have an unresolved close companion. Given this unusual optical signature, we reassess the possible connection with GB 790331. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/187553 Bibcode: 1994ApJ...433L..81I Keywords: Companion Stars; Gamma Ray Astronomy; Gamma Ray Bursts; Mira Variables; Nebulae; Astronomical Photography; Astronomical Spectroscopy; Charge Coupled Devices; Visible Spectrum; Astronomy; GAMMA RAYS: BURSTS; STARS: LATE-TYPE; STARS: MASS LOSS full text sources ADS | data products SIMBAD (2)

X-ray color image with the direct X-ray detection CCD

X-ray color image with the direct X-ray detection CCD

A measurement of the primordial helium abundance using MU Cassiopeiae

Speckle interferometric observations of the Population II astrometric binary star μ Cas have been made at four epochs with a direct imaging CCD system. Using the available orbital data on the system, the masses of the stars have been found to be 0.728 ± 0.049 M ⊙ and 0.171 ± 0.008 M ⊙ . Application of the theoretical mass-luminosity law to the primary yields a helium abundance of 0.23 ± 0.05 by mass for a metal abundance of Z = 0.0021 assuming a system age of 13 billion years

THE NYQUIST CRITERION IN CCD PHOTOMETRY FOR SURFACE BRIGHTNESS

ABSTRACT Astronomers routinely violate the directive to sample surface brightness with at least twice the frequency of the highest spatial frequency of the Fourier transform of the continuous image, when doing direct CCD imaging. It is reasonably speculated that this practice is rationalized on the basis that the CCD does not actually sample_ the surface brightness at periodic intervals, but instead integrates the surface brightness over contiguous regions (the CCD pixels). It is herein derived that this mode of sampling changes the form of aliasing error, but the aliasing error is nevertheless present when undersampling occurs. The very nature of the error betrays the possibility of detecting its presence, a priori. It would be of value to develop an active optical apodizer to accommodate a given CCD, in terms of the Nyquist criterion, without the need to abandon either the full light-gathering power of the telescope or the plate-scale at the chosen observing station.

OPTICAL OBSERVATIONS OF ADS 9193

ABSTRACT ADS 9193 was first cataloged as a visual binary by Herschel (1831), who reported a position angle of 165 deg and a separation of 5 arcsec for the system. Additional measurements up through 1966 have revealed little substantive change in these parameters. Optical spectra and UBV magnitudes obtained for both components of ADS 9193, as well as direct CCD image of the field containing these stars, confirm the previous findings for the astrometric characteristics of ADS 9193, and establish the spectral types of components A and B as M6/7 and F6, respectively. Although the probability that ADS 9193 is an optical double is low, the observed V magnitude difference is only half what would be expected if the stars are at a common distance of approximately 200 pc, assuming the primary is a giant and its companion is on the main sequence.

A new survey for quasar clustering

A photographic grism survey in a strip of sky 12.2 by 0.5 deg in extent and 6.1 sq deg in area was carried out in order to identify quasar candidates. Followup spectroscopy yielded a homogeneous sample of 127 quasars with z between 0.2 and 3.4 and median redshift of 1.93. Direct CCD observations were used to determine calibrated B(J) magnitudes. Positions, finding charts, and spectra are presented for the sample and for 24 additional quasars and emission-line galaxies contained in the survey. Analysis of the sample shows no evidence for clustering. The 1 sigma limit in the correlation function is 0.1-0.15 for r between 50 and 700 Mpc. 28 refs.

45. Stellar Classification

As an introduction to this report I would like to cite two comments from the book MK Process and Stellar Classification (ed. by R.F. Garrison, 1984). The first is from the article by W.W. Morgan The MK system and the MK process: “The MK system furnishes a satisfactory frame of reference for stars of Population I in the solar neighborhood; but when we consider the variety of stellar spectra encountered in our galaxy and in other stellar systems we are unable to classify many stars satisfactorily from the MK standards alone. What we now require is a more general frame of reference – or frames of reference – that will accept with precision a greater variety of ‘specimens’ (stellar spectra).” The second is an excerpt from one of the conclusions in the article by D.L. Crawford The relationship between the MK system and photometric classification: “The future potential of all this classification work is great. Technological change is rampant, and most interesting. New and powerful 1(λ) machines will be with us soon, as well as direct CCD photometers. Their power is great and we’ll all end up using them. The opening of new wavelength regions is a fantastic advantage to classifiers. The challenges and opportunities are vast.”During the last three years there have been technical improvements in CCD detectors and as a result they are now much better adapted to the needs of photometry and spectroscopy. Signal processing by modern computers now permits rapid utilization of large quantities of information. Technical progress in detectors and computer science now provides us with powerful and relatively low-cost tools for computation, and leads us to view with optimism the development of the powerful 1(A) machines anticipated by Crawford.

Discovery of an inner light-echo ring around SN 1987A

The detection of an inner light echo around SN 1987A based on observations made in January, 1989, is reported. An examination of direct CCD images reveals a third, inner light-echo ring around the SN with a mean radius of 8.2 arcsec and a width of the ring of 3.0 arcsec, so that the scattering material is distributed between radii 3.1 and 5.7 pc from the supernova. The difference in brightness on the eastern and western sides indicates that the scattering material is not uniformly distributed around the supernova. The inner light echo is attributed to a shell of red-supergiant wind material that was decelerated by its interaction with the surrounding medium. The fact that the discovery was made only in 1989 implies that there is a cavity in the dust along the line of sight toward the earth; therefore, the shell material outside the cavity became illuminated only at the end of 1988. 26 refs.

Imaging observations of gas and dust in NGC 4696 and implications for cooling flow models

Continuum and emission-line direct CCD observations of the gas and dust in NGC 4696 are analyzed. The wavelength-dependence of extinction is normal. Line luminosities are derived and evidence that the gas and dust are well-mixed is presented. A total power output of the dust lane of roughly 2 x 10 to the 43rd ergs/s is deduced. Constraints on the physical conditions and geometry in the emission-line gas are inferred. An external origin for the dust-lane material is favored from the observations; infall from a gas-rich companion with a normal interstellar medium may have recently taken place. The energy input to the dust and gas of the dust lane by saturated heat conduction from the hot X-ray gas is sufficient to power the optical and infrared emission. If conduction operates, the cool gas and dust act as a heat sink for the hot X-ray atmosphere and this may mimic some of the peripheral properties of a cooling flow. 57 refs.

A spiral galaxy at Z = 0.366 which overlaps the image of the quasar 4C 39.47

Direct CCD images in broad-band R and I have been obtained of the radio quasar 1632+391 [4C 39.46, z(emission) = 1.080] as part of an imaging survey of quasars at intermediate redshifts. A large, faint galaxy (FWHM = 4", R = 19.7) was identified which clearly overlaps the quasar's image. This galaxy is centered 4.2" east of the quasar, corresponding to 28 kpc at the galaxy's redshift (H = 50, q = 0). Detailed fits to the galaxy's luminosity profile demonstrated that it is a disk-dominated late-type spiral with an absolute B magnitude, -21.6, comparable to those of nearby Sc I galaxies such as M101. Low-dispersion spectroscopy of the galaxy yielded a redshift of z = 0.3662, based on Ca II H and K absorption and weak (O II] 3727 emission. The galaxy morphology and line emission imply the presence of appreciable interstellar gas in the superposed galaxy. High-dispersion, high signal-to-noise spectroscopy of the quasar would therefore provide an opportunity to study the interstellar medium in an identified galaxy at high redshift. A search for 21 cm absorption due to the galaxy would also be of great interest. Given the large apparent size of the galaxy, more detailed morphological study would be possible using observations from the Hubble Space Telescope.

CCD Images of Selected Planetary Nebulae

Direct interference filter CCD frames of a number of northern planetary nebulae were obtained at the Cassegrain focus of the 182-cm telescope of Asiago Astrophysical Observatory (Italy).

The Character of the Optical Variability for the BL Lacertae Objects OJ 287

The BL Lacertae objects, OJ 287, has long been known to exhibit large amplitude variations on time scales as short as a few days. The time rate of change in brightness for these variations has been observed to be in excess of 1.0 mag. per day on several occasions. However, the nature of the optical variations on time scales significantly shorter than a day has not been well established, and in many cases the results have been controversial (Carrasco et al, 1985, Lawrence et al 1987, McHardy and Czerny, 1987). In order to address this problem, we have obtained observations of OJ 287 on four different nights during the past two years using the KPNO 0.9 meter telescope equipped with the direct CCD camera. Variations were detected for OJ 287 on each night with ranges of 0.05 mag. to 0.10 mag. The variations detected on 1986 November 9 are typical of those observed on each of the nights and is shown in Figure 1. A power spectrum analysis of the data was performed and no convincing evidence for the presence of any periodicity was found. Based on this analysis, the short term optical variations observed for OJ 287 have a very different character than the rapid x-ray flickering observed for Seyfert galaxies which have been characterized by 1/f - noise. Therefore, these observations would imply sizes for the source region 3 × 10−5 pc. If one assures that the underlying engine is a supermassive blackhole, then the time scales of the variability suggests masses for the blackhole of 107M⊙ – 108M⊙.

Kinematics and ionization of extended gas in active galaxies. IV - The Seyfert 2 galaxy NGC 4388

We present the results of direct CCD imaging and long-slit, medium-dispersion spectroscopy of the extended narrow-line-emitting gas in the nearby Seyfert 2 galaxy NGC 4388, type SB(s)b pec. The spectra have been used to investigate the distribution, kinematics, and ionization structure of the excited gas in the regions surrounding the nucleus out to a distance of ~ 4.8 kpc. Our data support earlier suggestions that the galaxy, which appears to lie near the core of the Virgo cluster, has been tidally distorted, possibly by the nearby cluster core galaxies M84 or IC 3303. Much of the highly ionized gas in NGC 4388 appears to be distributed in two wide cones originating from the nucleus and extending above and below the disk. We observe line emission of this gas out to a projected height of ~ 1.5 kpc, although it appears to extend even higher. The overall velocity field of this gas and that lying within the disk is somewhat irregular, although a component of normal rotation about the nucleus is evident. Two isolated systems of high-ionization gas whose velocity are significantly discrepant from this velocity field are inferred to be material also lying well above the disk of the galaxy. These regions appear, however, to have different origins: the isolated patches of emission extending above the eastern spiral arm are likely the remnants of one or more recent supernovae, while the region situated directly to the north of the nucleus is interpreted as material which may have been ejected from the nucleus as it also coincident with a radio feature oriented perpendicular to the disk and extending 1.8 kpc from the optical nucleus. We offer three separate explanations of the presence of the remainder of the gas above and below the disk: (1) ejection from the nucleus, (2) removal from the disk by ram pressure and/or other processes arising from the interaction of the galaxy with the intracluster medium, and (3) accretion from a less massive galaxy during a recent tidal encounter. There are problems with each of these models individually and we feel the observed distribution and kinematics of the gas may be the result of a combination of these processes acting together.

Optical properties of cometary nuclei and a preliminary comparison with asteroids

view Abstract Citations (88) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Properties of Cometary Nuclei and a Preliminary Comparison with Asteroids Jewitt, D. C. ; Meech, K. J. Abstract Direct CCD observations of cometary nuclei are used to make a preliminary physical comparison with main-belt asteroids of comparable size. The nuclei have been studied within the past 2 yr using charge-coupled devices; the observations of P/Neujmin 1 and P/Tempel 2 are presented here for the first time. The photometric ranges of the nuclei are found to be larger than the ranges of typical main-belt asteroids of similar size, suggesting a systematic shape difference between the nuclei and the small asteroids. The shape difference may be a result of the different collisional histories of the nuclei and asteroids or of anisotropic sublimation of the nuclei. These and other possibilities are briefly discussed. From the scant available information it is suspected that the shapes of the nuclei may be more similar to the shapes of earth-crossing asteroids than to the shapes of main-belt asteroids, consistent with, but not proving, a common origin for the cometary nuclei and the earth-crossing asteroids. Publication: The Astrophysical Journal Pub Date: May 1988 DOI: 10.1086/166351 Bibcode: 1988ApJ...328..974J Keywords: Asteroid Belts; Charge Coupled Devices; Comet Nuclei; Comet Tails; Cross Sections; Physical Properties; COMETS; NUCLEI; OPTICAL PROPERTIES; COMPARISONS; CCD METHODS; ASTEROIDS; PHYSICAL PROPERTIES; NEUJMIN 1; TEMPEL 2; PHOTOMETRY; SIZE; SHAPE; EARTH-BASED OBSERVATIONS; COLLISIONS; SUBLIMATION; EARTH-CROSSERS; TELESCOPE METHODS; CALCULATIONS; HYPOTHESES; FORMATION; DENSITY; Astrophysics; Comets; ASTEROIDS; COMETS full text sources ADS |

Emission-line galaxies in the Bootes void

view Abstract Citations (64) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Emission-Line Galaxies in the Bootes Void Moody, J. Ward ; Kirshner, Robert P. ; MacAlpine, Gordon M. ; Gregory, Stephen A. Abstract The observation of three new Boo void emission-line galaxies (ELGs) in a 460-550-nm 4.5-deg prism survey, medium-dispersion spectra, and direct CCD R imagery is reported. The data are presented in tables, spectra, and isophotal maps along with data on five previously discovered Boo void ELGs. Six of the eight galaxies are shown to be similar to H II regions, with irregular morphologies, narrow lines, weak stellar continua, and diameters of about 10/h kpc; the other two are I Zw 81 (with a well-defined nucleus) and the Seyfert 1 spiral Mrk 845. The galaxy density of the void is estimated as no less than 10 percent of the cosmic mean galaxy density, and it is suggested that the fraction of ELGs in this region may be elevated. Publication: The Astrophysical Journal Pub Date: March 1987 DOI: 10.1086/184846 Bibcode: 1987ApJ...314L..33M Keywords: Emission Spectra; Galactic Clusters; Red Shift; Astronomical Spectroscopy; Galactic Structure; H Ii Regions; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: REDSHIFTS full text sources ADS | data products SIMBAD (9) NED (8)

Ultradeep Optical Identifications and Spectroscopy of Faint Radio Sources

During the last two years we have completed an extensive project of direct CCD imaging with the Palomar 200 inch Four-shooter on several milliJansky and microJansky radio samples, now totaling 200 sources. The purpose is to study the nature and redshift distribution of the radio galaxies that cause the upturn in the milliJansky source counts (WMOKK) and to search for candidates of primeval radio galaxies.

The detection of a circumstellar shell around P Cygni by direct CCD imaging

The star P Cygni (=HD 193237) is the proto-type of a class of stars with peculiar spectra, the so-called P-Cygni-stars (or Luminous Blue Variables). They are characterized by extreme mass-loss characteristics and wind densities surpassed only by the winds of Wolf-Rayet stars.