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J. Ge

Publications and source records attributed to J. Ge.

32 records · Page 2Linked to original sources
arXiv2012

Column density distribution and cosmological mass density of neutral gas: Sloan Digital Sky Survey-III Data Release 9

We present the first results from an ongoing survey for Damped Lyman-alpha systems (DLAs) in the spectra of z>2 quasars observed in the course of the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the Sloan Digital Sky Survey (SDSS) III. Our full (non-statistical) sample, based on Data Release 9, comprises 12,081 systems with log N(HI)>=20, out of which 6,839 have log N(HI)>=20.3. This is the largest DLA sample ever compiled, superseding that from SDSS-II by a factor of seven. Using a statistical sub-sample and estimating systematics from realistic mock data, we probe the N(HI) distribution at = 2.5. Contrary to what is generally believed, the distribution extends beyond 10^22 cm^-2 with a moderate slope of index\approx-3.5. This result matches surprisingly well the opacity-corrected distribution observed at z = 0. The cosmological mass density of neutral gas in DLAs is found to be Omega_g_DLA~10^-3, evolving only mildly over the past 12 billion years.

astro-ph.CO↗
arXiv2010

A Dusty Mg~II absorber Associated with the Quasar SDSS J003545.13+011441.2

We report on a dusty Mg~II absorber associated with the quasar SDSSJ003545.13+011441.2 (hereafter J0035+0114) at $z$=1.5501, which is the strongest one among the three Mg~II absorbers along the sight line of quasar. The two low redshift intervening absorbers are at $z$=0.7436, 0.5436, respectively. Based on the photometric and spectroscopic data of Sloan Digital Sky Survey (hereafter SDSS), we infer the rest frame color excess E(\bv) due to the associated dust is more than 0.07 by assuming a Small Magellanic Cloud (hereafter SMC) type extinction curve. Our follow-up moderate resolution spectroscopic observation at the 10-m Keck telescope with the ESI spectrometer enable us to reliably identify most of the important metal elements, such as Zn, Fe, Mn, Mg, Al, Si, Cr, and Ni in the associated system. We measure the column density of each species and detect significant dust depletion. In addition, we develop a simulation technique to gauge the significance of 2175-Å dust absorption bump on the SDSS quasar spectra. By using it, we analyze the SDSS spectrum of J0035+0114 for the presence of a associated 2175-Å extinction feature and report a tentative detection at $\sim$2$σ$ significant level.

astro-ph.CO↗
arXiv2010

A Near Infrared Laser Frequency Comb for High Precision Doppler Planet Surveys

We discuss the laser frequency comb as a near infrared astronomical wavelength reference, and describe progress towards a near infrared laser frequency comb at the National Institute of Standards and Technology and at the University of Colorado where we are operating a laser frequency comb suitable for use with a high resolution H band astronomical spectrograph.

astro-ph.IM↗
arXiv2009

Exoplanet Characterization and the Search for Life

Over 300 extrasolar planets (exoplanets) have been detected orbiting nearby stars. We now hope to conduct a census of all planets around nearby stars and to characterize their atmospheres and surfaces with spectroscopy. Rocky planets within their star's habitable zones have the highest priority, as these have the potential to harbor life. Our science goal is to find and characterize all nearby exoplanets; this requires that we measure the mass, orbit, and spectroscopic signature of each one at visible and infrared wavelengths. The techniques for doing this are at hand today. Within the decade we could answer long-standing questions about the evolution and nature of other planetary systems, and we could search for clues as to whether life exists elsewhere in our galactic neighborhood.

astro-ph.EP↗
arXiv2009

Global and local critical current density in superconducting SmFeAsO$_{1-x}$F$_x$ measured by two methods

The critical current densities of polycrystalline bulk SmFeAsO$_{1-x}$F$_x$ prepared by the powder-in-tube (PIT) method and by a conventional solid-state reaction were investigated using the remnant magnetic moment method and Campbell's method. Two types of shielding current, corresponding to global and local critical current densities $J_{\rm c}$ were observed using both measurement methods. The global and local $J_{\rm c}$ were on the order of $10^7$ A/m$^2$ and $10^{10}$ A/m$^2$ at 5 K, respectively. The local $J_{\rm c}$ decreased slightly with increasing magnetic field. The global $J_{\rm c}$ was independent of the preparation method, while the local $J_{\rm c}$ was larger for samples prepared by PIT than for those prepared by solid-state reaction.

cond-mat.supr-con↗
arXiv2008

Discovery of superstrong, fading, iron line emission and double-peaked Balmer lines of the galaxy SDSSJ0952+2143 - the light echo of a huge flare

We report the discovery of superstrong, fading, high-ionization iron line emission in the galaxy SDSSJ095209.56+214313.3 (SDSSJ0952+2143 hereafter), which must have been caused by an X-ray outburst of large amplitude. SDSSJ0952+2143 is unique in its strong multiwavelength variability; such a broadband emission-line and continuum response has not been observed before. The strong iron line emission is accompanied by unusual Balmer line emission with a broad base, narrow core and double-peaked narrow horns, and strong HeII emission. These lines, while strong in the SDSS spectrum taken in 2005, have faded away significantly in new spectra taken in December 2007. Comparison of SDSS, 2MASS, GALEX and follow-up GROND photometry reveals variability in the NUV, optical and NIR band. Taken together, these unusual observations can be explained by a giant outburst in the EUV--X-ray band, detected even in the optical and NIR. The intense and variable iron, Helium and Balmer lines represent the ``light echo'' of the flare, as it traveled through circumnuclear material. The outburst may have been caused by the tidal disruption of a star by a supermassive black hole. Spectroscopic surveys such as SDSS are well suited to detect emission-line light echoes of such rare flare events. Reverberation-mapping of these light echoes can then be used as a new and efficient probe of the physical conditions in the circumnuclear material in non-active or active galaxies.

astro-ph↗
arXiv2005

Cool Customers in the Stellar Graveyard III: Limits to Substellar Objects around nearby White Dwarfs using CFHT

Results from a groundbased high contrast imaging survey of thirteen nearby white dwarfs for substellar objects is presented. We place strict upper limits on the type of substellar objects present, ruling out the presence of anything larger than $\sim$14 M$_{Jup}$ for eight of the white dwarfs at separations $>$19 AU and corresponding to primordial separations of $\sim$3-6~AU assuming adiabatic mass loss without tidal interactions. With these results we place the first upper limit on the number of intermediate mass stars with brown dwarfs at separations $>$ 13 AU. We combine these results with previous work to place upper limits on the number of massive Jovian ($>$ 10 M$_{Jup}$) planets in orbit around white dwarfs whose progenitors spanned a mass range of 1-7 M$_{\odot}$.

astro-ph↗
arXiv2004

High Contrast Imaging with Gaussian Aperture Pupil Masks (GAPMs)

Gaussian aperture pupil masks (GAPMs) can in theory achieve the contrast requisite for directly imaging an extrasolar planet around a nearby solar type star. We outline the process of designing, fabricating, and testing a GAPM for use on current telescopes and specifically the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100$^{\prime\prime}$ telescope. We find that the initial prototype observations are quite successful, achieving a contrast similar to a traditional Lyot coronagraph without blocking any light from a central object and useful for finding faint companions to nearby young solar analogues. In the lab we can reproduce the expected PSF reasonably well and with a single aperture design which achieves $\sim4 \times 10^{-5}$ contrast at 10$λ/D$. We find that small inaccuracies in the mask fabrication process and insufficient correction of the atmosphere contribute the most degradation to contrast at these levels.

astro-ph↗
arXiv2004

Using Notch-Filter Masks for High Contrast Imaging of Extrasolar Planets

We present the first laboratory experiments using a notch-filter mask, a coronagraphic image mask that can produce infinite dynamic range in an ideal Lyot coronagraph according to scalar diffraction theory. We fabricated the first notch-filter mask prototype with .25 $\micron$ precision using an e-beam lithography machine. Our initial optical tests show that the prototype masks generate contrast levels of 10$^{-5}$ at 3$λ/D$ and 10$^{-6}$ at $\sim 8λ/D$, with a throughput of 27%. We speculate on the ``as-is'' performance of such a mask in the Hubble Space Telescope.

astro-ph↗
arXiv2003

First Planet Confirmation with a Dispersed Fixed-Delay Interferometer

The Exoplanet Tracker is a prototype of a new type of fibre-fed instrument for performing high precision relative Doppler measurements to detect extra-solar planets. A combination of Michelson interferometer and medium resolution spectrograph, this low-cost instrument facilitates radial velocity measurements with high throughput over a small bandwidth (~ 300 Angstroms), and has the potential to be designed for multi-object operation with moderate bandwidths (~1000 Angstroms). We present the first planet detection with this new type of instrument, a successful confirmation of the well established planetary companion to 51 Peg, showing an rms precision of 11.5m/s over five days. We also show comparison measurements of the radial velocity stable star, Eta Cas, showing an rms precision of 7.9m/s over seven days. These new results are starting to approach the precision levels obtained with traditional radial velocity techniques based on cross-dispersed echelles. We anticipate that this new technique could have an important impact in the search for extra-solar planets.

astro-ph↗
arXiv2003

High Contrast Imaging with Gaussian Aperture Pupil Masks

Gaussian aperture pupil masks (GAPMs) can in theory achieve the contrast requisite for directly imaging an extrasolar planet. We outline the process of fabricating and testing a GAPM for use on the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100$^{\prime\prime}$ telescope. We find that the initial prototype observations are quite successful, achieving a contrast similar to a traditional Lyot coronagraph witho ut blocking any light from a central object and useful for finding faint companions to nearby young solar analogues. In the lab we can reproduce the expected PSF to within an order of magnitude and with new designs achieve $\sim5 \times 10^{-5}$ contrast at 10$λ/D$. We find that small inaccuracies in the mask fabrication process and insufficient correction of the atmosphere contribute the most degradation to contrast. Finally we compare the performance of GAPMs and Lyot coronagraphs of similar throughput.

astro-ph↗
arXiv2002

First High Contrast Imaging Using a Gaussian Aperture Pupil Mask

Placing a pupil mask with a gaussian aperture into the optical train of current telescopes represents a way to attain high contrast imaging that potentially improves contrast by orders of magnitude compared to current techniques. We present here the first observations ever using a gaussian aperture pupil mask (GAPM) on the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100$^{\prime\prime}$ telescope. Two nearby stars were observed, $ε$ Eridani and $μ$ Her A. A faint companion was detected around $μ$ Her A, confirming it as a proper motion companion. Furthermore, the observed H and K magnitudes of the companion were used to constrain its nature. No companions or faint structure were observed for $ε$ Eridani. We found that our observations with the GAPM achieved contrast levels similar to our coronographic images, without blocking light from the central star. The mask's performance also nearly reached sensitivities reported for other ground based adaptive optics coronographs and deep HST images, but did not reach theoretically predicted contrast levels. We outline ways that could improve the performance of the GAPM by an order of magnitude or more.

astro-ph↗
arXiv2002

Nature of Faint Companions to G type Stars using Adaptive Optics

High spatial resolution (0.30 arcsec) NIR photometric observations using the adaptive optics of the 100 inch Mt. Wilson Telescope and the Penn State IR Imager and Spectrograph (PIRIS) have revealed faint companions to HD190067 and HIP13855. HD190067b is found to be of mass of 0.075$M_{\odot}$ to 0.1$M_{\odot}$ and with an age of 0.5 Gyrs to a few Gyrs. HIP13855b is a low mass star (age: 100 Myrs to 500 Myrs) of mass range between 0.1$M_{\odot}$ to 0.2$M_{\odot}$. Further NIR spectroscopic observations will be necessary to classify their spectral type precisely.

astro-ph↗