Publications of the Astronomical Society of the Pacific

van den Bergh, Sidney

doi: 10.1086/133070pmid: N/A

Distance determinations to individual galaxies, groups, and clusters are critically reviewed. All modern distance determinations have been reduced to a common and internally consistent system. These distances are then used to discuss the present status of the extragalactic distance scale and of the Hubble Parameter, HO. It is shown that the classical distance scale "problem" starts quite abruptly at D > 3 Mpc. It is emphasized that the reasons for this discrepancy are entirely independent of difficulties associated with large-scale deviations from a smooth Hubble flow. From eight different techniques the mean distance modulus of the Virgo cluster is found to be (m-M)o = 31.0 ± ).15 (D = 15.8 ± 1.1 Mpc). Twelve determinations of the difference between the distance moduli of the Coma and Virgo clusters yield Delta(m-M)o = 3.71 ± 0.05 mag and hence a Coma distance modulus (m-M)o = 34.71 ± 0.16 (D = 87 ± 6 Mpc). Combining this distance with the Coma cluster's cosmological velocity of 7210 km s-1 yields a value Ho (local) = 83 ± 6 km s-1 Mpc-1. From the velocity-distance relation for the brightest galaxies in clusters of Bautz-Morgan types I and I-II it is found that Ho (global)/Holocal = 0.92 ± 0.08, in which "local" refers to northern clusters with Vo < 10,000 km s-1. In other words the cluster data do not show a statistically significant difference between the local and global values of the Hubble parameter. If one nevertheless adopts Hoglobal/Holocal = 0.92 ± 0.08 then one obtains Hoglobal = 76 ± 9 km s-1 Mpc-1. This observed value of Ho differs at the 3 sigma level from that predicted by theories of stellar evolution in conjunction with canonical models of the Universe with Theta = 1 and Lambda = 0.

Lu, Meng; Scarfe, C. D.

doi: 10.1086/133071pmid: N/A

Photometric observations of SU Cephei were obtained with the 0.5 m telescope at the Climenhaga Observatory of the University of Victoria; a total of 152, well distributed over the light curve, were obtained in each of the B and V bands. In addition to yielding new light elements, the light curves provide information on the physical parameters of the system, by means of an analysis performed with Hill's (1979) LIGHT2 program. Although it does not permit us to constrain the mass ratio tightly, this preliminary photometric solution suggests that its value lies between 1.0 and 1.5, and that SU Cep is a contact binary.

Vanture, Andrew D.; Wallerstein, George

doi: 10.1086/133072pmid: N/A

An analysis of the CNO and s-process abundances in the M22 star III-106 has been completed. This star has been identified on the basis of DDO photometry by Hesser, Hartwick, and McClure, and on the basis of a low-resolution spectrum by McClure and Norris as a CH star. We find the star to have C = 7.1, N = 7.65,.

Smith, Graeme H.

doi: 10.1086/133073pmid: N/A

Echelle spectroscopy reported in the literature has provided evidence that the element oxygen is heterogeneously distributed within globular clusters. Star-to-star differences in the oxygen abundance have been identified in the clusters M92, M3, and M13 by Pilachowski; Brown, Wallerstein, and Oke; Sneden et al., and Kraft et al., and found to be accompanied by an O-N abundance anticorrelation. Such observations indicate that the material within the atmospheres and envelopes of the N-rich or CN-strong giants in these clusters has been processed through the CNO-bicycle of hydrogen burning. In this paper it is shown that the occurrence of variable amounts of interior O->N processing within metal-poor globular cluster red giants, such as those in M3 and M13, can also reconcile two other of the observed properties of these stars, namely the existence of a CN-C abundance anticorrelation yet substantial [C/Fe] depletions.

Schmidt, Edward G.; Chab, John R.; Reiswig, Darwin E.

doi: 10.1086/133074pmid: N/A

Photometric observations have been made of 16 stars classified as constant, CST or CST:, in the General Catalogue of Variable Stars. One star, U Tau, was found to be a rapid irregular variable and three others may vary at a low level. In two cases, FV Del and FP Gem, the star identified as the variable on published finding charts is not variable but a nearby star did vary. It is suggested that the wrong stars were marked on the charts but the possibility remains that the variables may have exhibited constancy during earlier observations.

Taylor, Benjamin J.; Joner, Michael D.

doi: 10.1086/133075pmid: N/A

We have compared the Hyades, Coma, and a set of field standard stars in the V and Stromgren-Beta systems. If Stromgren data by Crawford and his collaborators are considered, all the data turn out to be on the same system; no corrections as large as several mmag are required to achieve this state. For Beta, similar consistency between the Hyades and Coma is already known to exist. We find that for the standard stars, Beta values from the literature are consistent with the Hyades-Coma system. For V, we adopt corrections derived previously by Joner and Taylor for published cluster photometry. Given these corrections, we find that within rather generous accidental-error limits, the V systems for the field star and the clusters agree. With one puzzling exception (namely, b - y for the field stars and the Hyades), recent results published by Stetson agree with ours. Because our result is from direct comparison, we suggest that it should be preferred in this case. However, we also note the need for further comparison between our adopted standard stars and the Gronbech-Olsen stars which Stetson used.

Soker, Noam; Harpaz, Amos

doi: 10.1086/133076pmid: N/A

We apply a method, which is traditionally used for the solar magnetic field, to estimate the magnetic activity of AGB stars. We find that any magnetic field model which tries to explain axisymmetrical mass loss from single AGB stars encounters severe difficulties. This order of magnitude calculation suggests that megnetic activity in AGB stars could be significant only if the envelope is spun up by a binary companion. But then other effects due to the companion are likely to be more dominant than the magnetic activity. We then conduct a preliminary study of a possible mechanism by which a single star might lose mass axisymmetrically. The results suggest that as the envelope mass of an AGB star decreases to < 0.1 solar mass, the nature of the fundamental mode excitation could change. It is possible that, due to the same mechanism, higher order radial modes and nonradial p-modes could become significant to the mass loss process when the envelope mass becomes very low. We argue, however, that even this mechanism, if it works, requires a binary companion to spin up the AGB envelope.

Wurtz, Ron; Stocke, John T.

doi: 10.1086/133077pmid: N/A

We examined the use of liquid-crystal (LC) technology to build an easily reconfigurable focal-plane slit system for multi-object spectroscopy (MOS). Several kinds of LC screens were analyzed in a spectrophotometer and at the focus of the spectrograph on the 24-inch telescope at Sommers-Bausch Observatory (SBO) on the CU Boulder campus. Depending on the crystal material used, transmission can be as high as > 80% in the clear state across the visible spectrum, and constrast ratios (ratio of clear- to opaque-state transmission) of >100:1 can be attained, but high contrast and high transmission are not both present in the same LCs. While significant difficulties exist in fabricating LCs as competitive MOS focal plane slits, there exist no fundamental obstacles to implementing this technology in an astronomical setting. The major problems for currently avaiable LCs include: 1. In order to obtain clear-state transmission of > 80% across one free spectral order, even the best contrast ratios currently available for a single screen ( 100:1) are not good enough for faint-object spectroscopy. 2. To use the LC types which yield high clear-state transmission, thin-film transistors (TFTs) must be used to address individual pixels. Currently, development costs for such devices are quite high, though remanufacture costs are low. Based on our tests, by stacking two screens of the best LCs currently available, an LC MOS slit assembly could be configured to give a clear-state transmission of 50-70% across the optical band with off-state opacities approaching 10 magnitudes in that same range. While these specifications are already competitive with other MOS schemes currently in use, the major drawback of an LC MOS at this time appears to be obtaining sufficient opacity between slits to obtain accurate sky subtraction.

Horch, E.; Morgan, J. S.; Giaretta, G.; Kasle, D. B.

doi: 10.1086/133078pmid: N/A

We have developed a new system for making speckle observations with the Multi-Anode Michrochannel Array (MAMA) detector. This system is a true photon counting imaging device which records the arrival time of every detected photon and allows for reconstruction of image features near the diffraction limit of the telescope. We present a description of the system and summary of observational results obtained at the Lick Observatory 1-m reflector in September of 1991. The diffraction limit of the 1-m telescope at 5029 angstroms is about 0.125 arsec and we have successfully resolved the catalogued interferometric binary HD 202582 with a separation of 0.157 ± 0.031 arcsec. A pair of stars in the open cluster Chi Persei separated by 2.65 ± 0.22 arcsec with approximate V magnitudes 8.6 and 11.5 has also been successfully analyzed with the speckle technique.

Takami, Hideki; Shiba, Hisashi; Sato, Shuji; Yamashita, Takuya; Kobayashi, Yukiyasu

doi: 10.1086/133079pmid: N/A

A 16-channel, prism spectrophotopolarimeter (PSP) is described. It covers the near-infrared spectral region from 0.9 to 2.5 microns including the standard I, J, H, and K bands, with a resolution of approximately 0.1 microns. This spectrometer employs cooled field optics in order to alleviate wavelength shifts caused by differences of image positions in the diaphragm. The field optics, in cooperation with the simultaneity owing to the 16-channel linear array (15 InSbs plus a single Si-detector), enable us to achieve polarimetric accuracies as high as 0.2%. PSP is capable of quick conversion between photometric and polarimetric modes by inserting or retracting a half-wave plate and a wire grid polarizer in the optics. The detection limits of the photometric mode at the UH 2.2 m telescope atop Mauna Kea are 13.0, 12.6, 12.7, and 11.7 mg/Hz at the wavelength corresponding to the 0.94i, 1.18j, 1.62h, and 2.13k-band centers, respectively. Example of the observed data are presented.