ABSTRACT In order to look for large super-fast rotators, in late 2014 and early 2015, five dedicated surveys covering ∼188 deg2 in the ecliptic plane have been carried out in the R-band, with ∼10 ...minute cadence using the intermediate Palomar Transient Factory. Among 1029 reliable rotation periods obtained from the surveys, we discovered 1 new large super-fast rotator, (40511) 1999 RE88, and 18 other candidates. (40511) 1999 RE88 is an S-type inner main-belt asteroid with a diameter of D = 1.9 ± 0.3 km, a rotation period of P = 1.96 ± 0.01 hr, and a light curve amplitude of Δm ∼ 1.0 mag. To maintain such fast rotation, an internal cohesive strength of ∼780 Pa is required. Combining all known large super-fast rotators, their cohesive strengths all fall in the range of 100-1000 Pa of lunar regolith. However, the number of large super-fast rotators seems to be far less than the whole asteroid population. This might indicate a peculiar asteroid group for them. Although the detection efficiency for a long rotation period is greatly reduced due to our two-day observation time span, the spin-rate distributions of this work show consistent results with Chang et al. (2015), after considering the possible observational bias in our surveys. It shows a number decrease with an increase of spin rate for asteroids with a diameter of 3 ⩽ D ⩽ 15 km, and a number drop at a spin rate of f = 5 rev day−1 for asteroids with D ⩽ 3 km.
We report observations of a possible young transiting planet orbiting a previously known weak-lined T-Tauri star in the 7-10 Myr old Orion-OB1a/25-Ori region. The candidate was found as part of the ...Palomar Transient Factory (PTF) Orion project. It has a photometric transit period of 0.448413 + or - 0.000040 days, and appears in both 2009 and 2010 PTF data. Follow-up low-precision radial velocity (RV) observations and adaptive optics imaging suggest that the star is not an eclipsing binary, and that it is unlikely that a background source is blended with the target and mimicking the observed transit. RV observations with the Hobby-Eberly and Keck telescopes yield an RV that has the same period as the photometric event, but is offset in phase from the transit center by approx = - 0.22 periods. The amplitude (half range) of the RV variations is 2.4 km s super(-1) and is comparable with the expected RV amplitude that stellar spots could induce. The RV curve is likely dominated by stellar spot modulation and provides an upper limit to the projected companion mass of M sub(p) sin i sub(orb) <, ~4.8 + or - 1.2 M sub(Jup); when combined with the orbital inclination, i sub(orb), of the candidate planet from modeling of the transit light curve, we find an upper limit on the mass of the planetary candidate of M sub(p) <, ~5.5 + or - 1.4 M sub(Jup). This limit implies that the planet is orbiting close to, if not inside, its Roche limiting orbital radius, so that it may be undergoing active mass loss and evaporation.
Using the large multiwavelength data set in the Chandra/SWIRE Survey (0.6 deg super(2) in the Lockman Hole), we show evidence for the existence of highly obscured (Compton-thick) AGNs, estimate a ...lower limit to their surface density, and characterize their multiwavelength properties. Two independent selection methods based on the X-ray and infrared spectral properties are presented. The two selected samples contain (1) five X-ray sources with hard X-ray spectra and column densities 10 super(24) cm super(-2) and (2) 120 infrared sources with red and AGN-dominated infrared SEDs. We estimate a surface density of at least 25 Compton-thick AGNs deg super(-2) detected in the infrared in the Chandra/SWIRE field, of which 640% show distinct AGN signatures in their optical/near-infrared SEDs, the remaining being dominated by the host galaxy emission. Only 633% of all Compton-thick AGNs are detected in the X-rays at our depth F(0.3-8 keV) > 10 super(-15) ergs cm super(-2) s super(-1). We report the discovery of two sources in our sample of Compton-thick AGNs, SWIRE J104409.95+585224.8 (z = 2.54) and SWIRE J104406.30+583954.1 (z = 2.43), which are the most luminous Compton-thick AGNs at high z currently known. The properties of these two sources are discussed in detail with an analysis of their spectra, SEDs, luminosities, and black hole masses.
We use the Expanded Very Large Array to image radio continuum emission from local luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) in 1 GHz windows centered at 4.7, 7.2, 29, and 36 ...GHz. This allows us to probe the integrated radio spectral energy distribution (SED) of the most energetic galaxies in the local universe. The 4-8 GHz flux densities agree well with previous measurements. They yield spectral indices Delta *a --0.67 (where F Delta *n Delta *n Delta *a) with ?0.15 (1 Delta *s) scatter, typical of nonthermal (synchrotron) emission from star-forming galaxies. The contrast of our 4-8 GHz data with literature 1.5 and 8.4 GHz flux densities gives further evidence for curvature of the radio SED of U/LIRGs. The SED appears flatter near ~1 GHz than near ~6 GHz, suggesting significant optical depth effects at lower frequencies. The high-frequency (28-37 GHz) flux densities are low compared to extrapolations from the 4-8 GHz data. We confirm and extend to higher frequency a previously observed deficit of high-frequency radio emission for luminous starburst galaxies.
We report the discovery of two new halo velocity groups (Cancer groups A and B) traced by eight distant RR Lyrae stars and observed by the Palomar Transient Factory survey at R.A. ~ 129degrees, decl. ...~ 20degrees (l ~ 205degrees, b ~ 32degrees). Located at 92 kpc from the Galactic center (86 kpc from the Sun), these are some of the most distant substructures in the Galactic halo known to date. Follow-up spectroscopic observations with the Palomar Observatory 5.1 m Hale telescope and W. M. Keck Observatory 10 m Keck I telescope indicate that the two groups are moving away from the Galaxy at vA sub(gsr) = 78.0+ or -5.6 kms super(-1) (Cancer group A) and v super(B) sub(gsr) = 16.3+ or -7.1 kms super(-1) (Cancer group B). The groups have velocity dispersions of sigmaAvgsr = 12.4+ or -5.0 km s super(-1) and sigmaBvgsr = 14.9+ or -6.2 km s super(-1) and are spatially extended (about several kpc), making it very unlikely that they are bound systems, and more likely to be debris of tidally disrupted dwarf galaxies or globular clusters. Both groups are metal-poor (median metallicities of Fe/H super(A) = -1.6 dex and Fe/H super(B) = -2.1 dex) and have a somewhat uncertain (due to small sample size) metallicity dispersion of ~0.4 dex, suggesting dwarf galaxies as progenitors. Two additional RR Lyrae stars with velocities consistent with those of the Cancer groups have been observed ~25degrees east, suggesting possible extension of the groups in that direction.
The dominant non-instrumental background source for space-based infrared observatories is the zodiacal light (ZL). We present Spitzer Infrared Array Camera (IRAC) measurements of the ZL at 3.6, 4.5, ...5.8, and 8.0 mu m, taken as part of the instrument calibrations. We measure the changing surface brightness levels in approximately weekly IRAC observations near the north ecliptic pole over a period of roughly 8.5 years. This long time baseline is crucial for measuring the annual sinusoidal variation in the signal levels due to the tilt of the dust disk with respect to the ecliptic, which is the true signal of the ZL. This is compared to both Cosmic Background Explorer Diffuse Infrared Background Experiment data and a ZL model based thereon. Our data show a few-percent discrepancy from the Kelsall et al. model including a potential warping of the interplanetary dust disk and a previously detected overdensity in the dust cloud directly behind the Earth in its orbit. Accurate knowledge of the ZL is important for both extragalactic and Galactic astronomy including measurements of the cosmic infrared background, absolute measures of extended sources, and comparison to extrasolar interplanetary dust models. IRAC data can be used to further inform and test future ZL models.
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