Publications of the Astronomical Society of the Pacific

Trimble, Virginia; Leonard, Peter J. T.

doi: 10.1086/133510pmid: N/A

1994 was the year in which we saw the first images from the repaired Hubble Space Telescope; the probable detection of a diffuse intergalactic medium, a black hole in M87, and an enormous primordial deuterium abundance; the discovery of the first (and second) superluminal objects within our own galaxy; not to mention the demise of the Jovian dinosaurs. But, as always, most astronomers continued to work away on the projects that have interested them for years or decades, and we attempt also to report some progress in broader areas, including cooling flows, extragalactic globular cluster populations, disk instabilities, phases of the interstellar medium, and brown dwarfs among microlenses and other populations. Several sections of short items range from the obvious to the remarkable to the unbelievable. As in previous years, the ordering of the topics attempts to preserve the near-to-far custom of elementary astronomy textbooks.

Hale, Alan

doi: 10.1086/133511pmid: N/A

The results of a recent study of coplanarity tendencies between stellar equatorial and binary orbital planes are applied to the low-metal F9V star HD 114762, for which a possible substellar companion was reported by Latham et al. (1989). High-resolution spectroscopy is performed on HD 114762 in order to extract its projected rotational velocity (v sin i). This is then combined with an expected rotational velocity determined via age-scaling, providing an estimate of the star's equatorial inclination, which when combined with the results of the coplanarity study provides an approximate indication of the companion's orbital inclination. Although the former uncertainties in this process preclude an accurate estimate of the companion's inclination, the results suggest that the inclination is low, possibly low enough to force the companion's mass above the limit for hydrogen fusion. It is thus possible the companion may be nothing more exotic than a low-mass M star, as opposed to a brown dwarf. These results add support to a similar conclusion recently obtained by Cochran et al. (1991).

Joner, M. D.; Taylor, B. J.; Powell, J. M.; Johnson, S. B.

doi: 10.1086/133512pmid: N/A

In this paper, we consider the zero points of six sets of Stromgren-beta photometry. The color-index system to which our results are referred is a "Hyades-Coma" system composed of photometry by Crawford and Perry (1966, AJ, 71, 206) and Barnes (1960, AJ, 74, 407). For V magnitudes, we use measurements by Taylor and Joner (1992, PASP, 104, 911). Our results are as follows: (1) The zero points of photometry by Gronbech and Olsen (1976, A&AS, 25, 213; 1977, A&AS, 27, 443) are offset from those of the Hyades-Coma system. The offsets can amount to several mmag; they appear for V and all color indices except beta, and depend on right ascension and (usually) declination. (2) These offsets can be applied to photometry by Stetson (1991, AJ, 102, 589), who reduced his results to the Gronbech-Olsen system. After correction, Stetson's results for a set of "transfer stars" differ from comparable data published by Crawford and Barnes (1970, AJ, 75, 978). (3) A direct comparison of the transfer stars to the Hyades yields consistency between the Hyades-Coma and Crawford-Barnes zero points (for the transfer stars specifically). This result supports a conclusion drawn by Taylor and Joner, and suggests that there is some problem with the zero points of Stetson's transfer-star data. (4) From Stetson's corrected data, one finds that the Crawford-Perry zero points for the Hyades are consistent with the Crawford-Barnes zero points for Coma. This result agrees with a conclusion drawn by Taylor and Joner from their own data, and suggests that the problem postulated for Stetson's transfer-star data does not extend to his results for the Hyades and Coma.

Anthony-Twarog, Barbara J.; Twarog, Bruce A.; Craig, Jason

doi: 10.1086/133513pmid: N/A

We have obtained uvbyCa data for over 300 giants and horizontal branch stars in three fields of M22. The spread in (b-y) for the giant and horizontal branches is consistent with a spread in foreground reddening Delta-E (B-V) ~0.08. Reanalysis of the data of Norris and Freeman (1983) indicates not only positive correlations between CH, CN and a unimodal distribution for Ca. Our photometric indices, m1, and hk, demonstrate a range in metallicity that persists to two magnitudes below the horizontal branch, and confirm the correlation between calcium abundance and CN/CH. We infer from comparisons to spectroscopic data that m1 is dominated by the CN and CH abundance and find no independent evidence of a range in [Fe/H]. The excessive ranges in m1 and hk also suggest the influence of a continuous opacity source, reminiscent of the Bond-Neff effect, that is correlated with CNO abundance. The relative contributions of internal mixing and primordial variations for M22's giants are discussed.

Rosvick, J. M.; Davidge, T. J.

doi: 10.1086/133514pmid: N/A

Using the Dominion Astrophysical Observatory's 1.8 m telescope and infrared array detector, we have detected a near-infrared extended source embedded in the dark molecular cloud L1251. We measure the mean surface brightnesses in J, H and K to be 16.5, 14.1, and 14.1 magnitudes per square arcsecond, respectively. The central object is associated with the IRAS point source 22343+7501, and is composed of more than one source. Millimetre observations using the James Clerk Maxwell telescope yield integrated fluxes ranging from 0.23 (at 1.3 mm) to 0.71 (at 0.8 mm) Jy. Deep J and K' images taken with the Redeye detector on the Canada-France-Hawaii telescope show the source near the extended nebulosity to be multiple. The nebulosity contains a great deal of chaotic structure, and extends more than 30 arcseconds in J and over 20 arcseconds in K'. The line-of-sight absorption to IRAS 22343+7501 is estimated to be 32± 5 magnitudes, which is comparable to values found for similar objects. The spectral energy distribution is characteristic of an embedded source, and the range of fluxes at the different wavelengths imply that a single temperature for the cloud is not valid. The near-IR, far-IR and mm observations are consistent with the objects in this cloud being just past the protostar stage of evolution.

Weinberger, R.

doi: 10.1086/133515pmid: N/A

From a compliation of objects discovered during our long-term systematic searches on optical sky surveys, six particularly interesting objects have been selected. These hitherto unknown objects were investigated as to their optical appearance and seem to represent the following types of objects: a nearby dwarf irregular galaxy, a supernova remnant, a distant star cluster or nearby dwarf spheroidal galaxy, a galaxy clustering containing a bright "arc," a planetary nebula, and an extragalactic H II region. All the objects deserve detailed follow-up examination.

Libbrecht, K. G.; Peri, M. L.

doi: 10.1086/133516pmid: N/A

We describe a new fiber-fed echelle spectrograph which is now in operation on the Hale 5-meter telescope at Palomar Observatory. The instrument is optimized for high spectral stability, necessary for asteroseismology measurements of small periodic variations in stellar radial velocities. It features a 7-element all-spherical 610-mm focal length f/3.0 lens system and prism cross-disperser in a compact double-pass quasi-Littrow configuration. Light enters the system at prime focus, and is channeled to the spectrograph by a fiber optic cable. The instrument rests on a fixed-orientation optical bench inside the telescope's East Arm. It can be operated in a low-resolution mode, with resolution R=20,000 and overal efficiency (including atmospheric seeing) e~5 percent at 550 nm, or a high-resolution mode, with R=40,000 and e~1.5 percent at 550 nm; both modes have Rpixel=100,000. With large-format CCD detector (2048X2048 with 27-micron pixels), the entire visible spectrum from 400-1000 nm can be recorded in two exposures, with no gaps. We have also incorporated a novel imaging system to produce a circularly symmetric guide image of the input fiber tip. Using a fiber-optic double scrambler, the instrument produces radial-velocity measurements which are stable at the ~1 m/sec level over short (<~ 30 minute) time periods.

Gaffney, Niall I.; Lester, Dan F.; Doppmann, Gregg

doi: 10.1086/133517pmid: N/A

The shape and strength of the near infrared (2-0) 12CO absorption bandhead provides astronomers with a unique tool for measuring stellar kinematics in galaxies with strong dust obscuration. However, the asymmetric shape of the bandhead introduces complexities when extracting the kinematics from an observed spectrum. This paper discusses the benefits, drawbacks, and observational constraints associated with using this bandhead to measure kinematics in galaxies, focusing on applications in high spectral resolution data. Additionally, we discuss techniques found useful for extracting the kinematics from the absorption feature, and outline our success with two different mothods.

Aitken, G. J. M.; Johnson, R.; Meng, J.

doi: 10.1086/133518pmid: N/A

Truncation of the speckle cloud by the edges of an image detector causes significant artifacts and distortions in images reconstructed from their 2nd and 3rd-order spectra such as the Knox-Thompson (KT) and triple correlation (TC) bispectra. At high signal levels the near-axis, TC transfer function has a lower phase variance than the KT transfer function. This gives TC a higher dynamic range, an important property when observing detail. In both cases, the amount of improvement in image quality obtained by using additional bispectral planes increases with object complexity. Examples illustrate these properties.

Freudling, Wolfram

doi: 10.1086/133519pmid: N/A

A method is proposed to find and remove cosmic rays from stacks of images which are not registered. Such dithered images obtained with undersampling cameras, such as the Widefield and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope, can be used to recover some of the resolution lost by a large pixel size. The proposed method simultaneously cleans the images of cosmic rays and deconvolves them. Cosmic ray hits are dynamically identified at each iteration. The output is a combined and restored image and a list of cosmic ray hits for each of the input images. The final lists of cosmic ray hits are useful even if a restoration of the images is not desired. A simulated application of the method to WFPC2 images is presented.