We present photometric and spectroscopic observations of 23 high-redshift supernovae (SNe) spanning a range of z ¼ 0:34 1:03, nine of which are unambiguously classified as Type Ia. These SNe were discovered during the IfA Deep Survey, which began in 2001 September and observed a total of 2.5 deg 2 to a depth of approximately m % 25 26 in RIZ over 9-17 visits, typically every 1-3 weeks for nearly 5 months, with additional observations continuing until 2002 April. We give a brief description of the survey motivations, observational strategy, and reduction process. This sample of 23 high-redshift SNe includes 15 at z ! 0:7, doubling the published number of objects at these redshifts, and indicates that the evidence for acceleration of the universe is not due to a systematic effect proportional to redshift. In combination with the recent compilation of Tonry et al. (2003), we calculate cosmological parameter density contours that are consistent with the flat universe indicated by the cosmic microwave background (Spergel et al. 2003). Adopting the constraint that total ¼ 1:0, we obtain best-fit values of ð m ; Ã Þ ¼ ð0:33; 0:67Þ using 22 SNe from this survey augmented by the literature compilation. We show that using the empty-beam model for gravitational lensing does not eliminate the need for à > 0. Experience from this survey indicates great potential for similar large-scale surveys while also revealing the limitations of performing surveys for z > 1 SNe from the ground.

We have carried out a major survey for visual binaries towards the Orion Nebula Cluster using HST images obtained with an H-alpha filter. Among 781 likely ONC members more than 60" from theta-1 Ori C, we find 78 multiple systems (75 binaries and 3 triples), of which 55 are new discoveries, in the range from 0.1" to 1.5". About 9 binaries are likely line-of-sight associations. We find a binary fraction of 8.8%+-1.1% within the limited separation range from 67.5 to 675 AU. The field binary fraction in the same range is a factor 1.5 higher. Within the range 150 AU to 675 AU we find that T Tauri associations have a factor 2.2 more binaries than the ONC. The binary separation distribution function of the ONC shows unusual structure, with a sudden steep decrease in the number of binaries as the separation increases beyond 0.5", corresponding to 225 AU. We have measured the ratio of binaries wider than 0.5" to binaries closer than 0.5" as a function of distance from the Trapezium, and find that this ratio is significantly depressed in the inner region of the ONC. The deficit of wide binaries in the central part of the cluster is likely due to dissolution or orbital change during their passage through the potential well of the inner cluster region. Many of the companions are likely to be brown dwarfs.Comment: 27 pages, 10 figures, 2 tables, accepted by the Astronomical Journa

We have conducted a homogenous near-IR spectroscopic survey of 33 objects with varying degrees of similarity to FU Orionis.Common spectroscopic features that are characteristic of the three classical FUors FU Ori, V1057 Cyg, and V1515 Cyg are: strong CO absorption, weak metal absorption, strong water bands, low gravity, strong blue shifted He I absorption, and few (if any) emission lines. Based on these criteria, we classify the 33 objects as either bona fide FUors (eruption observed), FUor-like objects (eruption not observed), or peculiar objects with some FUor-like characteristics, and present a spectral atlas of 14 bona-fide FUors, 10 FUor-like objects, and 9 peculiar objects. All objects that we classify as FUors or FUor-like have very similar near-IR spectra. We use this spectral similarity to determine the extinction to each source, and correlate the extinction to the depth of the 3 µm ice band. All bona fide FUors still today maintain the spectrum of a FUor, despite the eruption occurring up to 80 years ago. Most FUors and FUor-like objects occupy a unique space on a plot of Na+Ca vs. CO equivalent widths, whereas the peculiar objects tend to be found mostly elsewhere. Since most FUors show a reflection nebula, we also present an atlas of K-band images of each target. We found that the near-IR spectra of FUors and young brown dwarfs can be extremely similar, a distinguishing feature being the Paschen β absorption in the spectra of FUors. Although V1647 Ori, AR 6a, and V346 Normae had been previously classified as candidate FUors, we classify them as peculiar objects with some FUor-like properties since their spectra now differ significantly from bona fide FUors. We confirm two new FUor-like objects that were initially identified as candidates based on their near-IR morphology.

We present the results of a near-IR spectroscopic survey of 110 Class I protostars observed from 0.80 μm to 2.43 μm at a spectroscopic resolution of R = 1200. This survey is unique in its selection of targets from the whole sky, its sample size, wavelength coverage, depth, and sample selection. We find that Class I objects exhibit a wide range of lines and the continuum spectroscopic features. Eighty-five percent of Class I protostars exhibit features indicative of mass accretion, and we found that the veiling excess, CO emission, and Br γ emission are closely related. We modeled the spectra to estimate the veiling excess (r k ) and extinction to each target. We also used near-IR colors and emission line ratios, when available, to also estimate extinction. In the course of this survey, we observed the spectra of 10 FU Orionis-like objects, including 2 new ones, as well as 3 Herbig Ae-type stars among our Class I young stellar objects. We used photospheric absorption lines, when available, to estimate the spectral type of each target. Although most targets are late-type stars, there are several A-and F-type stars in our sample. Notably, we found no A or F class stars in the Taurus-Auriga or Perseus star-forming regions. There are several cases where the observed CO and/or water absorption bands are deeper than expected from the photospheric spectral type. We find a correlation between the appearance of the reflection nebula, which traces the distribution of material on very large scales, and the near-IR spectrum, which probes smaller scales. All of the FU Orionis-like objects are associated with reflection nebulae. The spectra of the components of spatially resolved protostellar binaries tend to be very similar. In particular both components tend to have similar veiling and H 2 emission, inconsistent with random selection from the sample as a whole. There is a strong correlation between [Fe ii] and H 2 emission, supporting previous results showing that H 2 emission in the spectra of young stars is usually shock excited by stellar winds.