Publications of the Astronomical Society of the Pacific

Candia, P.; Krisciunas, K.; Suntzeff, Nicholas B.; González, D.; Espinoza, J.; Leiton, R.; Rest, A.; Smith, R. C.; Cuadra, J.; Tavenner, T.; Logan, C.; Snider, K.; Thomas, M.; West, A. A.; González, G.; González, S.; Phillips, M. M.; Hastings, N. C.; McMillan, R.

doi: 10.1086/368229pmid: N/A

We present optical and infrared photometry of the unusual Type Ia supernova 2000cx. With the data of Li et al. and Jha, this constitutes the largest data set ever assembled for a Type Ia SN, more than 600 points in UBVRIJHK. We confirm the finding of Li et al. regarding the unusually blue B−V colors as SN 2000cx entered the nebular phase. Its I‐band secondary hump was extremely weak given its B‐band decline rate. The V minus near‐infrared colors likewise do not match loci based on other slowly declining Type Ia SNe, although V−K is the least “abnormal.” In several ways, SN 2000cx resembles other slow decliners, given its B‐band decline rate [Δm15(B) = 0.93], the appearance of Fe iii lines and weakness of Si ii in its premaximum spectrum, the V−K colors, and postmaximum V−H colors. If the distance modulus derived from surface brightness fluctuations of the host galaxy is correct, we find that the rate of light increase prior to maximum, the characteristics of the bolometric light curve, and the implied absolute magnitude at maximum are all consistent with a subluminous object with Δm15(B) ≈ 1.6–1.7 having a higher than normal kinetic energy.

Fugal, Jacob P.; Moody, J. Ward

doi: 10.1086/368100pmid: N/A

We examine the issues surrounding an IR slitless prism survey for galaxies with highly redshifted Hα to see if some of the next generation of IR instruments should have the capability to conduct such surveys. We model the galaxy and star surface density as a function of J, H, and K magnitudes to estimate field crowding with depth. Using data from the Subaru 8.2 m telescope and Infrared Camera and Spectrograph detector as a benchmark, we estimate the number of detectable galaxies as a function of telescope aperture size, object magnitude, and line strength. We find that while crowding need not be a major problem, it is still difficult for even a large telescope to obtain a useful emission‐line galaxy sample in the J, H, or K bands primarily because of the high IR background and the faintness of the galaxies with Hα in these bands.

Trac, Hy; Pen, Ue‐Li

doi: 10.1086/367747pmid: N/A

We present a pedagogical review of some of the methods employed in Eulerian computational fluid dynamics (CFD). Fluid mechanics is governed by the Euler equations, which are conservation laws for mass, momentum, and energy. The standard approach to Eulerian CFD is to divide space into finite volumes or cells and store the cell‐averaged values of conserved hydro quantities. The integral Euler equations are then solved by computing the flux of the mass, momentum, and energy across cell boundaries. We review both first‐order and second‐order flux assignment schemes. All linear schemes are either dispersive or diffusive. The nonlinear, second‐order accurate total variation diminishing (TVD) approach provides high‐resolution capturing of shocks and prevents unphysical oscillations. We review the relaxing TVD scheme, a simple and robust method to solve systems of conservation laws such as the Euler equations. A three‐dimensional relaxing TVD code is applied to the Sedov‐Taylor blast‐wave test. The propagation of the blast wave is accurately captured and the shock front is sharply resolved. We apply a three‐dimensional self‐gravitating hydro code to simulating the formation of blue straggler stars through stellar mergers and present some numerical results. A sample three‐dimensional relaxing TVD code is provided in the Appendix.

Kenworthy, M. A.; Hinz, P. M.

doi: 10.1086/368099pmid: N/A

High‐precision spectrophotometry is highly desirable in detecting and characterizing close‐in extrasolar planets to learn about their makeup and temperature. For such a goal, a modest‐size telescope with a simple low‐resolution spectroscopic instrument is potentially as good as or better than a complex general‐purpose spectrograph since calibration and removal of systematic errors are expected to dominate. We use a transmission grating placed in front of an imaging CCD camera on Steward Observatory’s Kuiper 1.5 m telescope to provide a high signal‐to‐noise ratio, low‐dispersion visible spectrum of the star HD 209458. We attempt to detect the reflected light signal from the extrasolar planet HD 209458b by differencing the signal just before and after secondary occultation. We present a simple data reduction method and explore the limits of ground‐based low‐dispersion spectrophotometry with a diffraction grating. Reflected light detection levels of 0.1% are achievable for 5000–7000 Å, too coarse for useful limits on extrasolar planets but potentially useful for determining spectra of short‐period binary systems with large (Δmvis = 6) brightness ratios. Limits on the precision are set by variations in atmospheric seeing in the low‐resolution spectrum. Calibration of this effect can be carried out by measurement of atmospheric parameters from the observations themselves, which may allow the precision to be limited by the noise due to photon statistics and atmospheric scintillation effects.

Matt, Sean; Böhm, Karl‐Heinz

doi: 10.1086/367744pmid: N/A

To gain insight into the nature of the peculiar Herbig‐Haro object HH 255 (also called Burnham's nebula), we use previously published observations to derive information about the emission‐line fluxes as a function of position within HH 255 and compare them with the well‐studied and relatively well behaved bow shock HH 1. There are some qualitative similarities in the Hα and [O iii] λ5007 lines in both objects. However, in contrast to the expectation of the standard bow‐shock model, the fluxes of the [O i] λ6300, [S ii] λ6731, and [N ii] λ6583 lines are essentially constant along the axis of the flow, while the electron density decreases, over a large distance within HH 255. We also explore the possibility that HH 255 represents the emission behind a standing or quasi‐stationary shock. The shock faces upwind, and we suggest, using theoretical arguments, that it may be associated with the collimation of the southern outflow from T Tauri. Using a simplified magnetohydrodynamic simulation to illustrate the basic concept, we demonstrate that the existence of such a shock at the north edge of HH 255 could indeed explain its unusual kinematic and ionization properties. Whether or not such a shock can explain the detailed emission‐line stratification remains an open question.

Smith, Nathan; Morse, Jon A.; Bally, John; Phelps, Randy L.

doi: 10.1086/368098pmid: N/A

We discuss optical and infrared emission from the putative planetary nebula in the young open cluster NGC 3572. Velocity images of [N ii] λ6583 obtained with the Rutgers/CTIO Fabry‐Perot interferometer reveal that most gas in the nebula is expanding at velocities ≲5 km s -1, with marginal evidence for bipolar expansion. A few outer condensations are seen at faster redshifted velocities, but their origin is uncertain. Optical spectra reveal a spatial excitation gradient, with higher excitation in a diffuse outer halo and low excitation in the bright inner nebula, suggesting that the nebula is externally ionized by hot stars in the open cluster and that the nebula and cluster are therefore equidistant. The nebula coincides with an infrared source detected by the MSX and IRAS satellites and has a spectral energy distribution implying a total mass of 5–10 M⊙. MSX also reveals diffuse infrared emission associated with the cluster, and its morphology implies a connection with the ring nebula. We discuss two very different interpretations of this object—it is either a strange planetary nebula or (more probably) a young photoevaporating globule left over from the molecular cloud that formed the cluster.

MacConnell, D. Jack

doi: 10.1086/367743pmid: N/A

A large set of deep, near‐IR, objective‐prism plates taken along the southern Galactic plane was searched for cool supergiants and carbon stars. Accurate coordinates and charts for 759 carbon stars in two Galactic longitude sectors within 7.°5 of the plane, 248°<l<288° and 320°<l<341°, are given, including 289 stars not previously published. Many of the new and known stars are found in the IRAS, DENIS, and 2MASS point‐source catalogs. The 2MASS colors and the longitude distribution of cool carbon stars are discussed briefly.

Ren, D.; Rimmele, T. R.; Hegwer, S.; Murray, L.

doi: 10.1086/367746pmid: N/A

A new and innovative single‐mode fiber interferometer is proposed for the wave‐front test of the adaptive optics (AO) system. It is based on a modified Mach‐Zehnder interferometer with the two arms replaced by optical fibers. It avoids the difficulty of fringe interpretation of the conventional Mach‐Zehnder interferometer. As fibers are used, the whole instrument is compact, flexible, and suitable for the AO on‐site test. Furthermore, as minimum optical components are used, the interferometer is free of calibration and has high measurement accuracy. The operation of the interferometer is also very simple, and wave front can be tested quickly. We discuss the working principle, experiment setup, fringe analysis, and its application for an existing AO system. The interferometer can also be used to test wave aberrations of a single lens or an optical system.

Rayner, J. T.; Toomey, D. W.; Onaka, P. M.; Denault, A. J.; Stahlberger, W. E.; Vacca, W. D.; Cushing, M. C.; Wang, S.

doi: 10.1086/367745pmid: N/A

We present the design, construction, and performance of SpeX, a medium‐resolution 0.8–5.5 μm cryogenic spectrograph and imager, now in operation at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The design uses prism cross‐dispersers and gratings to provide resolving powers up to R∼2000 simultaneously across 0.8–2.4, 1.9–4.2, or 2.4–5.5 μm, with a 15″ long slit. A high‐throughput low‐resolution R∼200 prism mode is also provided for faint‐object and occultation spectroscopy. Single‐order 60″ long‐slit modes with resolving powers up to R∼2000 are available for extended objects. The spectrograph employs an Aladdin 3 1024 × 1024 InSb array and uses narrow slits and a spatial scale of 0.″15 pixel -1 for optimum sensitivity on point sources. An autonomous infrared slit viewer is used for object acquisition, infrared guiding, and scientific imaging in the wavelength range 0.8–5.5 μm. The imager employs an Aladdin 2 512 × 512 InSb array that covers a 60′′ × 60′′ field of view at 0.″12 pixel -1. SpeX was successfully commissioned on IRTF during 2000 May, June, and July. Astronomical observations are presented to illustrate performance.

Peterson, J. B.; Radford, S. J. E.; Ade, P. A. R.; Chamberlin, R. A.; O’Kelly, M. J.; Peterson, K. M.; Schartman, E.

doi: 10.1086/368101pmid: N/A

The summit of Mauna Kea in Hawaii, the area near Cerro Chajnantor in Chile, and the South Pole are sites of large millimeter‐ or submillimeter‐wavelength telescopes. We have placed 860 GHz sky brightness monitors at all three sites and present a comparative study of the measured submillimeter brightness due to atmospheric thermal emission. We report the stability of that quantity at each site.