Jane X. Luu

BVRI Light Curves for 22 Type 1a Supernovae

We present 1210 Johnson/Cousins B, V, R, and I photometric observations of 22 recent Type Ia supernovae (SNe Ia): SNe 1993ac, 1993ae, 1994M, 1994S, 1994T, 1994Q, 1994ae, 1995D, 1995E, 1995al, 1995ac, 1995ak, 1995bd, 1996C, 1996X, 1996Z, 1996ab, 1996ai, 1996bk, 1996bl, 1996bo, and 1996bv. Most of the photometry was obtained at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics in a cooperative observing plan aimed at improving the database for SNe Ia. The redshifts of the sample range from cz = 1200 to 37,000 km s-1 with a mean of cz = 7000 km s-1.

Ubvri light curves of 44 type ia supernovae

We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is the largest homogeneously observed and reduced sample of SNe Ia to date, nearly doubling the number of well-observed, nearby SNe Ia with published multicolor CCD light curves. The large sample of U-band photometry is a unique addition, with important connections to SNe Ia observed at high redshift. The decline rate of SN Ia U-band light curves correlates well with the decline rate in other bands, as does the U - B color at maximum light. However, the U-band peak magnitudes show an increased dispersion relative to other bands even after accounting for extinction and decline rate, amounting to an additional ~40% intrinsic scatter compared to the B band.

Crystalline water ice on the Kuiper belt object (50000) Quaoar

The Kuiper belt is a disk-like structure consisting of solid bodies orbiting the Sun beyond Neptune. It is the source of the short-period comets and the likely repository of the Solar Systems most primitive materials. Surface temperatures in the belt are low (∼ 50u2009K), suggesting that ices trapped at formation should have been preserved over the age of the Solar System. Unfortunately, most Kuiper belt objects are too faint for meaningful compositional study, even with the largest available telescopes. Water ice has been reported in a handful of objects, but most appear spectrally featureless. Here we report near-infrared observations of the large Kuiper belt object (50000) Quaoar, which reveal the presence of crystalline water ice and ammonia hydrate. Crystallinity indicates that the ice has been heated to at least 110u2009K. Both ammonia hydrate and crystalline water ice should be destroyed by energetic particle irradiation on a timescale of about 107u2009yr. We conclude that Quaoar has been recently resurfaced, either by impact exposure of previously buried (shielded) ices or by cryovolcanic outgassing, or by a combination of these processes.

LARGE KUIPER BELT OBJECTS: THE MAUNA KEA 8K CCD SURVEY

We describe a large-area ecliptic survey designed to assess the sky-plane surface density of bright Kuiper Belt objects. We used an 8192 ) 8192 pixel CCD mosaic to image 51.5 deg2 to a 50% detection threshold red magnitude Thirteen new Kuiper Belt objects were identi—ed in the survey, m R 22.5. including some of the brightest and, presumably, largest known examples. We use Monte Carlo models to assess the eUects of observational bias in our survey and to examine (1) the size distribution of bright objects in the Kuiper Belt, (2) the possible existence of a cutoU in the size distribution at large radii, (3) the intrinsic ratio of Plutinos to nonresonant (ii classical ˇˇ) Kuiper Belt objects, (4) the intrinsic ratio of populations in the 3:2 and 2:1 mean motion resonances, and (5) the radial extent of the Kuiper Belt.

Accretion in the Early Kuiper Belt. I. Coagulation and Velocity Evolution

We describe planetesimal accretion calculations in the Kuiper Belt. Our evolution code simulates planetesimal growth in a single annulus and includes velocity evolution but not fragmentation. Test results match analytic solutions and duplicate previous simulations at 1 AU. In the Kuiper Belt, simulations without velocity evolution produce a single runaway body with a radius ri 1000 km on a timscale τr ∝ Me, where M0 is the initial mass in the annulus, e0 is the initial eccentricity of the planetesimals, and x ≈ 1–2. Runaway growth occurs in 100 Myr for M0 ≈ 10ME and e0 ≈ 10-3 in a 6 AU annulus centered at 35 AU. This mass is close to the amount of dusty material expected in a minimum-mass solar nebula extrapolated into the Kuiper Belt. Simulations with velocity evolution produce runaway growth on a wide range of timescales. Dynamical friction and viscous stirring increase particle velocities in models with large (8 km radius) initial bodies. This velocity increase delays runaway growth by a factor of 2 compared with models without velocity evolution. In contrast, collisional damping dominates over dynamical friction and viscous stirring in models with small (80–800 m) initial bodies. Collisional damping decreases the timescale to runaway growth by factors of 4–10 relative to constant-velocity calculations. Simulations with minimum-mass solar nebulae, M0 ~ 10ME, and small eccentricities, e ≈ 10-3, reach runaway growth on timescales of 20–40 Myr with 80 m initial bodies, 50–100 Myr with 800 m bodies, and 75–250 Myr for 8 km initial bodies. These growth times vary linearly with the mass of the annulus, τr ∝ M, but are less sensitive to the initial eccentricity than constant-velocity models. In both sets of models, the timescales to produce 1000+ km objects are comparable to estimated formation timescales for Neptune. Thus, Pluto-sized objects can form in the outer solar system in parallel with the condensation of the outermost large planets.

A new dynamical class of object in the outer Solar System

Some three dozen objects have now been discovered beyond the orbit of Neptune and classified as members of the Kuiper belt—a remnant population of icy planetesimals that failed to be incorporated into planets. At still greater distances is believed to lie the Oort cloud—a massive population of cometary objects distributed approximately in a sphere of characteristic dimension 50,000au(ref. 6). Here we report the discovery of an object, 1996TL66, that appears to be representative of a population of scattered bodies located between the Kuiper belt and the Oort cloud. 1996TL66has an orbital semimajor axis of 84au, and is in an extremely eccentric and highly inclined orbit (e = 0.58, i = 24°). With a red magnitude ∼20.9, it is the brightest trans-neptunian object yet found since Pluto and Charon. Its discovery suggests that the Kuiper belt extends substantially beyond the 30–50auregion sampled by previous surveys, and may contain much more mass than previously suspected.

Optical-Infrared Spectral Diversity in the Kuiper Belt

We have measured the optical and infrared colors of five Kuiper belt objects to search for evidence of spectral diversity among these bodies. We find extreme differences, especially in the measured V - J color indices, that indicate a wide range of surface compositions in the Kuiper belt.

The new BL Lacertae objects discovered by an efficient X-ray/radio/optical technique

The discovery of 13 serendipitous BL Lac objects in the Einstein IPC Slew Survey by means of x ray/radio vs. x ray/optical color-color diagrams and confirmation by optical spectroscopy are reported. These 13 BL Lacs were discovered using a technique which exploits the characteristic broad band spectra of BL Lacs. New VLA detections provide accurate fluxes (f(6 cm) is approximately 0.5 mJy) and 2 in. positions, facilitating the determination of an optical counterpart. All 13 new BL Lacs show essentially featureless optical spectra. Nine of these lie within the range of colors of known x ray selected BL Lacs. Of the remaining four, one is apparently x ray louder (by a factor of 1.5) or optically quieter (by 0.8 mags); and three are optically louder (by 1-1.3 mags) than x ray selected BL Lacs. Approximately 50 new BL Lacs in total are expected from VLA work and upcoming Australia Telescope observations, yielding a complete Slew Survey sample of approximately 90 BL Lacs.

A CCD portrait of Comet P/Tempel 2

The development of activity in Comet P/Tempel 2 is studied from aphelion (R = 4 AU) to perihelion (R = 1.4 AU) using extensive time-series CCD photometry and CCD spectra. The comet undergoes a profound morphological change at R of about 2-2.5 AU, from a bare nucleus at larger distances to an active comet supporting a coma of gas and dust. Cyclic photometric variations with the period T = 8.95 + or - 0.01 hr. are present at all R, and are attributed to the rotation of the nucleus at this period. The nucleus is prolate (axes a:b:c = 1.9:1:1), a property shared with other nuclei studied using CCD photometry. Novel results include a limit on the bulk density of the nucleus, rho above 300 kg/cu m, and a 20-A-resolution CCD spectrum of the nucleus. Spatially and temporally resolved photometry is used to study the effects of nucleus rotation on the coma. The coma does not share the dramatic photometric variations shown by the nucleus. It possesses a steep surface-brightness distribution, which is attributable to progressive destruction of the coma grains with increasing space exposure. 41 refs.

Optical and Infrared Reflectance Spectrum of Kuiper Belt Object 1996 TL66

We have obtained optical (0.4-0.8 μm) and near-infrared (1.0-2.5 μm) reflectance spectra of the Kuiper Belt object 1996 TL66. The spectra show no evidence for absorption features and are neutral across the full wavelength range. The spectrum of TL66 is thus similar to that of the Centaur Chiron but different from that of the Centaur Pholus. It also bears no resemblance to the spectrum of the Kuiper Belt object 1993 SC reported by Brown et al. (1997).