We report here optical observations during the September/October 1998 outburst of the black hole candidate XTE J1550-564. CCD photometry was obtained for the optical counterpart with the 0.9m Dutch telescope at La Silla since the onset of this event. We analysed 211 U, V and i frames, from Sep 10 to Oct 23. Stochastic flaring activity was observed on Sep 11-16, but no evidence for a superhump period, as seen in other soft X-ray transients, was found. An optical flare nearly simultaneous to an X-ray flare that occurred on Sep 21 was observed in the V-band. A reddened optical spectrum showed the typical emission lines corresponding to X-ray transients in outburst. From the interstellar absorption lines, we derive E(B-V) = 0.70 +/- 0.10 and suggest D approximate to 2.5 kpc. In such case, M-B approximate to +7 mag. for the progenitor, which is consistent with the spectral type of a low-mass similar to K0-K5 main-sequence companion.

We present a catalog of extremely red objects (EROs) discovered using the Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (NICMOS) parallel imaging database and ground-based optical follow-up observations. Within an area of 16 arcmin(2), we detect 15 objects with R-F160W > 5 and F160W < 21.5. We have also obtained K-band photometry for a subset of the 15 EROs. All of the R-F160W selected EROs imaged at K-band have R-K > 6. Our objects have F110W-F160W colors in the range 1.3-2.1, redder than the cluster elliptical galaxies at z similar to 0.8 and nearly 1 mag redder than the average population selected from the F160W images at the same depth. In addition, among only 22 NICMOS pointings, we detected two groups or clusters in two fields; each contains three or more EROs, suggesting that extremely red galaxies may be strongly clustered. At bright magnitudes with F160W < 19.5, the ERO surface density is similar to what has been measured by other surveys. At the limit of our sample, F160W = 21.5, our measured surface density is 0.94 +/- 0.24 arcmin(-2). Excluding the two possible groups or clusters and the one apparently stellar object reduces the surface density to 0.38 +/- 0.15 arcmin(-2).

An increasing number of observations have shown that dusty starburst. galaxies are probably much more numerous at high redshifts than today, and optical surveys of the distant universe suffer from large extinction corrections. In this talk, I present the quantitative estimate on how much dust extinction correction needed to apply to the rest-frame UV luminosity density at z similar to 1.3. In addition, I will discuss the recent deep 1.4GHz radio observations of extremely red galaxies (EROs), covering an area of 26 x 26 with complimentary deep optical and near-IR images. We found that the fraction of bright EROs (H G 20) detected in deep 1.4GHz images is small, only 8-17%. The implication is that a large fraction of bright EROs are probably old ellipticals or systems with a small amount of star forming activities at z similar to 1 - 2. We found that similar to 20% of well detected micro-Jansky radio sources are very faint or even not detected in the optical and near-IR. These faint micro-Jansky sources have H > 20.5 and K > 19.5 - 20. The interpretation of these optically faint, micro-Jansky radio sources is that they are potentially candidates of dust enshrouded starburst galaxies beyond a redshift of 1. Our 1.4GHz detection threshold of 40muJy (5sigma) sets the minimum limit of star formation activities of - 200M(circle dot)/yr at z - 1.5, which can be probed by our deep VLA data. An increasing number of recent observations [2,4] support our speculation that optically faint, micro-Jansky radio sources are potential dusty starbursts at high redshift. This may be the most efficient way of detecting a large sample of sub-mm sources with the current available instruments.

Optical spectra of 14 emission-line galaxies representative of the 1999 NICMOS parallel grism Halpha survey of McCarthy et al. are presented. Of the 14, 9 have emission lines confirming the redshifts found in the grism survey. The higher resolution of our optical spectra improves the redshift accuracy by a factor of 5. The [O II]/Halpha values of our sample are found to be more than 2 times lower than expected from Jansen et al. This [O II]/Halpha ratio discrepancy is most likely explained by additional reddening in our Halpha-selected sample [on average, as much as an extra E(B-V)=0.6], as well as by a possible stronger dependence of the [O II]/Halpha ratio on galaxy luminosity than is found in local galaxies. The result is that star formation rates (SFRs) calculated from [O II]lambda3727 emission, uncorrected for extinction, are found to be on average 4+/-2 times lower than the SFRs calculated from Halpha emission. Classification of emission-line galaxies as starburst or Seyfert galaxies based on comparison of the ratios [O II]/Hbeta and [Ne III]lambda3869/Hbeta is discussed. New Seyfert 1 diagnostics using the Halpha line luminosity, H-band absolute magnitude, and Halpha equivalent widths are also presented. One galaxy is classified as a Seyfert 1 based on its broad emission lines, implying a comoving number density for Seyfert 1 galaxies of 2.5(-2.1)(+5.9)x10(-5) Mpc(-3). This comoving number density is a factor of 2.4(-2.0)(+5.5) times higher than estimated by other surveys.

We have selected 14 J-dropout Lyman break galaxy (LBG) candidates with J(110) - H-160 >= 2.5 from the NICMOS Parallel Imaging Survey. This survey consists of 135 arcmin(2) of imaging in 228 independent sight lines, reaching average 5 sigma sensitivities of J(110) = 25.8 and H-160 = 25.6 (AB). Distinguishing these candidates from dust-reddened star-forming galaxies at z similar to 2-3 is difficult and will require longer wavelength observations. We consider the likelihood that any J-dropout LBGs exist in this survey and find that if L*(z=9.5) is significantly brighter than L*(z=6) ( a factor of 4), then a few J-dropout LBGs are likely. A similar increase in luminosity has been suggested by Eyles et al. and Yan et al., but the magnitude of this increase is uncertain.

We determine the global star formation rate (SFR) density at 0.7 < z < 1.9 using emission-line-selected galaxies identified in Hubble Space Telescope-Near Infrared Camera and Multi-Object Spectrograph (HST-NICMOS) grism spectroscopy observations. Observing in a pure parallel mode throughout HST Cycles 12 and 13, our survey covers similar to 104 arcmin(2) from which we select 80 galaxies with likely redshifted H alpha emission lines. In several cases, a somewhat weaker [O III] doublet emission is also detected. The Ha luminosity range of the emission-line galaxy sample is 4.4 x 10(41) < L(H alpha) < 1.5 x 10(43) erg s(-1). In this range, the luminosity function is well described by a Schechter function with phi* = ( 4.24 +/- 3.55) x 10(-3) Mpc(-3), L* = (2.88 +/- 1.58) x 10(42) erg s(-1), and alpha = -1.39 +/- 0.43. We derive a volume-averaged SFR density of 0.138 +/- 0.058 M(circle dot) yr(-1) Mpc(-3) at z = 1.4 without an extinction correction. Subdividing the redshift range, we find SFR densities of 0.088 +/- 0.056 M(circle dot) yr(-1) Mpc(-3) at z = 1.1 and 0.265 +/- 0.174 M(circle dot) yr(-1) Mpc(-3) at z = 1.6. The overall star formation rate density is consistent with previous studies using Ha when the same average extinction correction is applied, confirming that the cosmic peak of star formation occurs at z > 1.5.

We present a structural characterization of solid germane (GeH4) under pressure from first-principles calculations. We find that this material undertakes a structural transformation from its low-pressure P2(1)/c phase to high-pressure Cmmm phase at about 15GPa where insulator-metal transition occurs, followed by two other metallic phases having the P2(1)/m and C2/c structure at up to 200GPa. Our results indicate that the metallization of GeH4 can be realized through band overlap within the material itself. Copyright (c) EPLA, 2010

We report the first results from the Hubble Infrared Pure Parallel Imaging Extragalactic Survey, which utilizes the pure parallel orbits of the Hubble Space Telescope to do deep imaging along a large number of random sightlines. To date, our analysis includes 26 widely separated fields observed by the Wide Field Camera 3, which amounts to 122.8 arcmin(2) in total area. We have found three bright Y-098-dropouts, which are candidate galaxies at z greater than or similar to 7.4. One of these objects shows an indication of peculiar variability and its nature is uncertain. The other two objects are among the brightest candidate galaxies at these redshifts known to date (L > 2L*). Such very luminous objects could be the progenitors of the high-mass Lyman break galaxies observed at lower redshifts (up to z similar to 5). While our sample is still limited in size, it is much less subject to the uncertainty caused by "cosmic variance" than other samples because it is derived using fields along many random sightlines. We find that the existence of the brightest candidate at z approximate to 7.4 is not well explained by the current luminosity function (LF) estimates at z approximate to 8. However, its inferred surface density could be explained by the prediction from the LFs at z approximate to 7 if it belongs to the high-redshift tail of the galaxy population at z approximate to 7.

We present a sample of 17 newly discovered ultracool dwarf candidates later than similar to M8, drawn from 231.90 arcmin(2) of Hubble Space Telescope Wide Field Camera 3 infrared imaging. By comparing the observed number counts for 17.5 <= J(125) <= 25.5 AB mag to an exponential disk model, we estimate a vertical scale height of z(scl) = 290 +/- 25 (random) +/- 31 (systematic) pc for a binarity fraction of f(b) = 0. While our estimate is roughly consistent with published results, we suggest that the differences can be attributed to sample properties, with the present sample containing far more substellar objects than previous work. We predict the object counts should peak at J(125) similar to 24 AB mag due to the exponentially declining number density at the edge of the disk. We conclude by arguing that trend in scale height with spectral type may breakdown for brown dwarfs since they do not settle onto the main sequence.

Carbon can exist as isolated dumbbell, 1D chain, 2D plane, and 3D network in carbon solids or carbon-based compounds, which attributes to its rich chemical binding way, including sp-, sp(2)-, and sp(3)-hybridized bonds. sp(2)-hybridizing carbon always captures special attention due to its unique physical and chemical property. Here, using an evolutionary algorithm in conjunction with ab initio method, we found that, under compression, dumbbell carbon in CaC2 can be polymerized first into 1D chain and then into ribbon and further into 2D graphite sheet at higher pressure. The C2/m structure transforms into an orthorhombic Cmcm phase at 0.5 GPa, followed by another orthorhombic Immm phase, which is stabilized in a wide pressure range of 15.2-105.8 GPa and then forced into MgB2-type phase with wide range stability up to at least 1 TPa. Strong electron-phonon coupling. in compressed CaC2 is found, in particular for Immm phase, which has the highest lambda value (0.562-0.564) among them, leading to its high superconducting critical temperature T-c (7.9 similar to 9.8 K), which is comparable with the 11.5 K value of CaC6. Our results show that calcium not only can stabilize carbon sp(2) hybridization at a larger range of pressure but also can contribute in superconducting behavior, which would further ignite experimental and theoretical interest in alkaline-earth metal carbides to uncover their peculiar physical properties under extreme conditions.