Research Projects


Our research activities are mainly concentrated on searching for exoplanets and brown dwarfs, observing high reshshift quasar absorbers and developing innovative  techniques and instrumentation for cutting-edge astronomical observations.

OBSERVATION

Dharma Planet Survey

The SDSS-III Multi-object APO Radial Velocity Exoplanet Survey (MARVELS)

Observational Cosmology and Quasar Absorption Line Systems
Gamma Ray Burst Afterglows 
 

TELESCOPE, INSTRUMENTATION AND TECHNOLOGY

 

50in Automatic Telescope
TOU Very High Resolution Optical Spectrograph
Florida IR Silicon immersion grating spectromeTer (FIRST)
EXPERT and LiJET
Silicon Immersion Grating Technology
Michelson Type Fixed-delay Interferometers


Dharma Planet Survey     Back

The Dharma Planet Survey (DPS), funded by Dharma Endowment Foundation, is designed to detect and characterize close-in low-mass planets and sub-Jovian planets at the orbital region (~200-450 days) amenable to future space-imaging missions. The ultimate survey goal is to detect potentially habitable super-Earth planet candidates to independently measure η and provide high priority targets for future space direct-imaging missions (such as WFIRST-AFTA and LUVOIR surveyor) to identify possible biomarkers supporting life (Ge et al. 2014). It will initially search for and characterize low-mass planets around 150 nearby bright FGKM dwarfs (34 late F, 66 G dwarfs, 30 K dwarfs with V<7, and  20 M dwarfs with V<10 and within ~25 pc, Figure 2.1) in 2016-2020, and then continue to monitor targets with linear trends and observe more targets after 2020.

The DPS survey adopts a totally different strategy than previous low-mass planet surveys using ground-based Doppler spectrographs (Howard et al. 2010 & Mayor et al. 2011). Instead of surveying a large number of targets with variable number of measurements (from a few RV data points to ~400 RV data points, e.g., Dumusque et al. 2012), the DPS survey will offer a homogeneous high cadence for every survey target, i.e., about 100 RV measurements randomly spread over 450 days (about one measurement every other night for a typical survey target after excluding the Arizona Monsoon season and bad weather).

The automatic nature of the 50inch telescope, the Dharma Endowment Foundation Telescope (DEFT), and its flexible queue observation schedule are key to realizing this homogenous high cadence. This cadence will minimize the time-aliasing in detecting low-mass planets, especially those in highly eccentric orbits, which can be missed by previous surveys. Because of the homogenous cadence for every survey star, both detections and non-detections from the survey can be reliably used for statistical studies. Thus, the proposed survey strategy, cadence, and schedule will offer the best accuracy to assess the survey completeness and to determine occurrence rates of low-mass planets. As illustrated, our survey strategy allows for probing most of the parameter space in the planet mass-period distribution of nearby bright FGK and M dwarfs to independently verify characteristics (such as distribution, orbital properties, stellar properties, and occurrence rates) of the close-in low-mass planet population. It also covers the periods ~200-450 days, which are critical for the upcoming WFIRST-AFTA and LUVOIR direct-imaging missions. This survey will offer the best homogeneous data set for constraining formation models of low-mass planets with periods less than 450 days.

This DPS survey strategy provides an efficient way to explore habitable low-mass planets around nearby FGKM shown in the following Figure with greatly improved survey sensitivity and completeness compared to previous Doppler surveys. The DPS can reach planets masses ~10 times smaller (50% completeness) in the habitable zones around FGK dwarfs than reached by previous RV surveys reported in Howard & Fulton (2014), even under the pessimistic RV survey performance (~2 m/s). Improved measurements of η of nearby FGK dwarfs will help establish a global view of habitable worlds in the solar neighborhood.

2.1. Survey Target Selection: Our survey targets were selected from the following catalogs: Gliese Catalog of Nearby Stars (Spring 1989); Gliese Catalog of Nearby Stars cross identified with 2MASS (Stauffer et al. 2010); ROSAT All-Sky Survey: Nearby Stars (Huensch et al. 1999).  

-    Spectral type: ~F5V-K7V.

-    Brightest stars in each subtype that satisfy the following criteria:

o   No stellar companions within 5

o   vsini < 3 km/s

o   RV jitter < 2 m/s (for GK dwarfs, and < 3 m/s for F dwarfs) if available

o   In active stars, using any available indicators.

  log RHK < -4.85

  ratio between X-ray luminosity and bolometric luminosity, Rx < -3.0, if activity level is unknown

o   < 30 RV observations with better than 3 m/s Doppler precision if observed before

o   RAs are equally distributed from 0-360 deg. and DECs are between -20 and 90 deg.

The above figures shows magnitude and effective temperature distributions of our selected targets. 44 of 100 targets are in the Eta-Earth Survey list and eight planets have been detected among these 44 Eta-Earth survey stars. Some adjustment of targets, including vetting out of target candidates with RV jitters > 2 m/s (except > 3 m/s for F dwarfs), will be made to optimize the survey efficiency and sensitivity before the full survey starts.

 

FIRST NIR M Dwarf survey:

In collaboration with Drs. Matt Muterspaugh (TSU), Cullen Blake (UPENN), Rory Barnes (Univ. of Washington) and a former Ph.D student, Ji Wang (Yale), we plan to conduct the FIRST NIR M dwarf planet survey with the AST 2m robotic telescope at Fairborn Observatory. The survey instrument is the Florida IR Silicon immersion grating spectromeTer (FIRST), which was developed in 2009-2013. This new generation cryogenic IR spectrograph offers broad-band high resolution IR spectroscopy with R=68,000 at 1.4-1.8 mm and R=55,000 at 0.8-1.35 mm in a single exposure with a 2kx2k H2RG IR array. It is enabled by a compact design using an extremely high dispersion silicon immersion grating (SIG) and an R4 echelle with a 50 mm diameter pupil in combination with an Image Slicer.

 

The FIRST NIR M dwarf survey is the first large-scale NIR high precision Doppler survey dedicated to detecting and characterizing planets around 200 nearby M dwarfs with J< 10. The predicted instrument long term Doppler precision is about 3 m/s including measurement errors from photon noise, calibration and telluric absorption and emission lines. Our primary science goal is to look for habitable super-Earths around the late M dwarfs and also to identify transiting systems for follow-up observations with JWST to measure the planetary atmospheric compositions and study their habitability. Our secondary science goal is to detect and characterize a large number of planets around M dwarfs to understand the statistics of planet populations around these low mass stars and constrain planet formation and evolution models. Our survey baseline is expected to detect ~30 exoplanets, including 10 Super Earths, within 100 day periods. About half of the super-Earths are in their habitable zones. The AST, with its robotic control and ease of switching between instruments (in seconds), enables great flexibility and efficiency, and enables an optimal strategy, in terms of schedule and cadence, for this NIR M dwarf planet survey.

 

Figure below shows Late M dwarf orbit period vs. stellar host mass to be explored by the FIRST survey. The shaded regions are the HZ, with darker regions corresponding to less constraint for habitability (i.e., 0%, 50% to 100% cloud coverage, respectively). The dashed (dotted) curves show where planets induce a 4 m/s (2 m/s) reflex velocity in the star, assuming a circular orbit. The left most curve is for a 1 Earth-mass planet, then 5, then 10. FIRST can detect planets to the left of the curve.

 

 

 

 Back to Top

Observational Cosmology and quasar absorption line systems    Back

Dust grains play a key role in the astrophysical processes in the Universe. The amount of dust attenuation is a key parameter to accurately derive star formation rates from the rest frame ultraviolet (UV) spectra. Measuring the dust extinction curve and making a corresponding dust reddening correction allows the accurate determination of the intrinsic Spectral Energy Distributions (SEDs), galaxy, AGN and quasar luminosity functions, photometric redshifts and physical properties of galaxies. In spite of its importance, dust extinction in both low and high redshift galaxies is poorly known.

 The most remarkable and intriguing feature in the dust UV extinction curve is the broad 2175 absorption bump, or called the UV bump. It is observed ubiquitously in the Milky Way (MW) and Large Magellanic Clouds (LMC). The origin of the bump, its dependence on environment, and its evolution have been a mystery for the past 46 years since its discovery.

In collaborations with Drs. Shaohua Zhang (PRIC), Hongyan Zhou (PRIC), Peng Jiang (USTC), Dr. Jian Ge and his student, Jingzhe Ma, have identified a new population of quasar absorption line systems (QALs), called quasar 2175 dust absorbers, at z~0.7-2.4 in SDSS and SDSS-III BOSS quasar spectra. These absorbers have a distinguishing broad UV bump at 2175 in the underlying shape of the quasar spectra, similar to that seen in Milky Way diffuse clouds. The following figure shows a typical broad 2175 UV bump in a SDSS quasar spectrum.

Our quasar 2175 absorber identification technique is called the quasar spectra pair method (Wang et al. 2004, ApJ, 609, 589; Jiang et al. 2011, ApJ, 732, 110). The reddened spectrum is an observed quasar spectrum, and the unreddened is replaced by the SDSS DR7 quasar composite spectrum (Figure 2.1.1, Jiang et al. 2011) by combining 105,783 quasar spectra in the SDSS DR7 database.

Our fitting has three major steps:

1)      Determination of the linear component of the extinction curve: we fit the observed quasar spectrum using a reddened composite quasar spectrum by an extinction curve without an UV bump feature.

2)      Modeling the parameterized extinction curve: The parameters of the UV bump feature are limited to the peak position, 4.4mm-1 < x0 < 4.8mm-1, and the bump width 0.5mm-1 <g< 2.7mm-1, where x0 and g is the peak position and full width at half maximum (FWHM) of the Drude profile, respectively. The constraints are determined according to the distribution of the parameters measured on Galactic and LMC2 supershell region (Fitzpatrick & Massa 2007, Gordon et al. 2003).

3)       Remodeling of the spectra and candidate selection: We reject the spectral regions with offsets>3s between the observed and the reddened composite quasar spectrum, and refit the spectra to identify a possible UV bump candidate.

After the candidates are identified, we perform an independent verification approach to gauge the significance of the extinction bumps using a simulation technique developed by Jiang et al. (2010, ApJ, 724, 1325). The simulation technique begins with the selection of a control sample of SDSS quasar spectra at a similar redshift to the quasar of interest. Then we fit each of them by reddening the composite quasar spectrum with a parameterized extinction curve at the absorber redshift. The parameters x0 and γ in the parameterized extinction curve are fixed to the best values fitting the 2175 extinction bump of interest. The distribution of bump strengths is expected to be Gaussian by assuming random fluctuations in the continuum of each spectrum in the control sample. If the bump strength of the absorber lies far off this distribution, then the detection of a bump has statistical significance as shown in the following figure.

We only choose bumps reaching at least 3s significance level as detections. Our Monte Carlo simulations show that this technique can efficiently identify strong 2175 absorbers (≥3s significance level) in the SDSS spectroscopic database to better than 90% completeness (Jiang et al. 2011; Zhang et al. 2012 in preparation).

 

To date, we have identified a total of 429 quasar 2175 dust absorbers. These data are being used for statistical studies of the properties of these rare quasar absorbers. The absorption lines associated with these objects allow us to study the interstellar medium in great detail to understand their physical and chemical conditions and processes.

In collaboration of a large international collaboration team, including Drs. Jason Prochaska (UCSC), Pasquier Noterdaeme (Institut dAstrophysique de Paris  (IAP), Anand Sriannand (Inter-University Centre for Astronomy and Astrophysics), Fred Hamann (UF), Don York (Chicago), Bruce Draine (Princeton), Nic Ross (LBL), Xiaohui Fan (UA), Michael Strauss (Princeton), Eilat Glikman (Yale), Don Schneider (PSU), Niel Brandt (PSU), Carolin Villforth (UF), and Britt Lundgren (Yale), we are working on following up some of the quasar 2175 dust absorbers at Keck, VLT and other large telescopes. The following figure shows velocity profiles of metal lines for the 2175  absorption system toward quasar J1459+0024, a representative quasar 2175 dust absorbers. All of these absorbers show high metallicities, approaching the MW value, and also high depletion of refractory elements, such as Cr, Fe, Ti, and Ni, indicating high dust content in the system.

 

Our ultimate goal with this project is to understand the nature of the quasar 2175 dust absorbers. The results of this investigation will address extinction biases associated with quasar absorption line systems and will cast light on the physics of dust grains at different cosmic epochs. This project offers a global perspective on the formation and characteristics of dust in the ISM of high z galaxies.

Back to Top

 

High Redshift Gamma Ray Burst Afterglows   Back

We (Jian Ge, Bing Zhang (UNLV), Matt Muterspaugh (TSU), Bo Zhao and graduate students) are preparing the FIRST plus an IFU for performing ground-based follow-up observations of the Gamma-ray burst (GRB) sources detected by the Swift GRB mission. The high sensitivity of FIRST IFU and quick instrument response (within 2 min) at the AST 2m robotic telescope will enable the capture of the brightest phase of the GRB afterglows, to obtain high-resolution spectrum (R ~ 1000) of the afterglow, and to measure their redshifts. The data will permit a study of spectral features associated with GRB hosts or intergalactic medium, probe the prompt emission phase, and investigate bridges between the prompt emission phase and afterglow phase. Unlike most of the ground-based follow-up observations that are limited to optical wavelengths, our observations will be conducted in the near-IR (0.8-1.8 microns). GRBs at redshifts between z=5.6-13.8 will be identified through detecting the unique strong Lyman alpha absorption trough due to the Gunn-Peterson effect. Detection of these high redshift objects will provide one of the most powerful tools for investigating the first generation of star formation and the reionization era in the early universe. IR observations can also help to identify many GRBs deeply embedded in the dusty environment and reveal the nature of the progenitors of GRBs at moderate redshifts.

FIRST coupled with the AST 2m robotic telescope has the ability and the unique advantage to fulfill this task, before the use of the JWST for such an exciting study. Assuming that the GRBs at z = 5.6-13.8 have the same afterglow luminosity as those at z = 0.3 -4.5, FIRST can detect most of them at a spectral resolving power of R ~ 1000 within ~1-2 hours after the bursts.  During the ground-based GRB follow-up observations, we will also provide sub arsec precision coordinate information of the GRBs to GRB Coordinates Network (GCN), allowing quick follow-up afterglow observations by other groups all over the world.

  Back to Top

Instrumentation Projects

Florida IR Silicon immersion grating spectromeTer (FIRST)    Back

FIRST is a next generation, fiber-fed, highly stable (temperature controlled), cryogenic, NIR high-resolution, cross-dispersed echelle spectrograph operated in a vacuum chamber (Ge et al. 2012, Proc. SPIE, 8446E, 3OG). The FIRST instrument is being integrated and tested in the UF SAIL lab. The following figure shows the assembled instrument in the lab. FIRST has two channels: a red channel with a UF made silicon immersion grating (SIG) as the main disperser to simultaneously cover 1.4-1.8 m at R=68K and a blue channel with a commercial R4 echelle to cover 0.8-1.35 m at R=56K. The red channel will be primarily used for the SIG high-resolution spectroscopy technology demonstration while the blue channel will be used for the M dwarf survey observations (science). The spectra are recorded with an H2RG 2K2K array from Teledyne Technologies Inc with 2.57 m wavelength cutoff. The detector is controlled by the standard Teledyne ASIC card. The entire instrument bench (1.04x0.45 meter in dimension) is installed inside a vacuum chamber. A 30-layer MALI thermal shield is mounted around the bench to thermally insulate the bench from the chamber. The optical bench is cooled with three cryotigers using standard NF-55 gas and operates at 193K to reduce the thermal background while the detector is cooled by one cryotiger with PT-13 gas and runs at 77K to reduce its dark current. The entire instrument temperature is to be precisely controlled to within 4 mK over a long term. The instrument will be placed inside a temperature-controlled instrument room at Fairborn Observatory with yearly temperature variation within 2C to further reduce the instrument long-term temperature variations.

                            

FIRST is fed with three 80 m diameter fibers (2.1 arcsec on sky, one science, one sky and one calibration) at f/4. The science beam is sliced into two halves by a Mirror Image Slicer developed from the traditional Bowen-Walraven Image Slicer and passes through the spectrograph entrance slit (half of the calibration and sky fiber beams is blocked to produce the same spectral resolution as the science beam). The FIRST blue channel covers 31 spectral orders (orders 46-76, see the figure below) at 0.8-1.35 m with 95% wavelength coverage while the red channel completely covers 59 spectral orders (orders 195-253, see the figure below) at 1.4-1.8 m. Two broad band sorting filters on a motorized rotation stage are used to select an observation channel. The following table summarizes FIRST instrument parameters.

FIRST is calibrated with a tungsten lamp for flatfielding and an UrNe lamp for wavelength and RV calibration and instrument point spread function modeling. In order to precisely calibrate instrument drift to reach high RV precision (~4 m/s), a separate UrNe spectrum is recorded at the same time as a star spectrum. An UrNe exposure is also taken through the science fiber before and after each star exposure to remove residual drifts not corrected by the simultaneous separate beam calibration. Since the UrNe calibration lamp, like a ThAr lamp, has limited lifetime, frequent replacement of the UrNe calibration lamp requires calibrating offsets for different lamps. This offset calibration is made by shining a second UrNe lamp used occasionally (such as twice per month). Fibers (science and calibration fibers) are mode scrambled by an optical mode scrambler to reduce illumination-induced variations in the RV measurements.

Wavelength region

0.8-1.8 m

Focal plane

2048x2048 H2RG

Pixel size

18 m

Detector QE

81% 0.6-1.0 m

90% 1.0-2.4 m

Spectral resolution

R=56K at 0.8-1.35 m (Blue)

R=68K at 1.4-1.8 m (Red)

Dispersion per pixel

0.10/pix at 1.25 m (Blue)

0.11 /pix at 1.65 m (Red)

Sampling

2.1 pixels

Fiber diameter

2.1 arcsec (80 m)

Spectral orders

46-76 (0.8-1.35 m) (Blue)

195-253 (1.4-1.8 m) (Red)

Single exposure coverage

0.52 m at 0.8-1.35 um (Blue)

0.4 m at 1.4-1.8 m (Red)

Design type

White pupil + refractive camera

Collimated beam

50 mm in diameter

Main dispersers

R4, 31.6 l/mm, 76 blaze (Blue)

SIG, 16.1 l/mm, 54.74 blaze (Red)

Cross-dispersers

(VPH gratings)

240 l/mm 7.0 blaze (Blue)

310 l/mm, 14.0 blaze (Red)

Optical bench

1.04x0.45 meter

Back to Top

 

EXPERT-III Very High Resolution Optical Spectrograph Back

EXPERT-III is a new generation, fiber-fed, highly stable, optical extremely high resolution, cross-dispersed echelle spectrograph operated in a vacuum chamber (see the figure below). It has two spectral resolution modes: an Extremely High Resolution (EHR) mode with R~100,000 and a High Resolution (HR) mode with R~50,000. The EHR mode is designed for providing extremely high Doppler precision measurements of bright GKM dwarfs (V<9) while the HR mode is for obtaining spectra of relatively faint stars. The HR mode can also be used for providing high precision RV measurements of relatively faint FGKM stars (9<V<15). A commercial R4 (76 deg blaze angle) echelle with a 112x408mm ruled area is used as the main disperser and two prisms made of PBM18Y glass are used as the cross-disperser. The spectra from 0.38-0.9 m are recorded with a 4kx4k Fairchild back-illuminated CCD array. The detector completely covers spectra from 0.38-0.8 m and nearly completely covers 0.8-0.9 m (only the edges of the dispersed spectra are off the detector). The detector is controlled by the Leach controller from Astronomical Research Cameras, Inc. The entire instrument bench (1.34x0.8 meter in dimension) is installed inside a vacuum chamber with a volume of 1.46x0.85x0.48 m3. The chamber is inside a thermal enclosure where temperatures are precisely controlled to provide a long term thermal stability of the instrument. Small heaters and Lakeshore temperature sensors are placed on the bench (four corners and the central region) and the detector assembly to allow the bench and detector temperature precisely controlled. The CCD detector is cooled by one cryotiger with PT-30 gas and runs at -100C to reduce its dark current. The entire instrument system will be placed inside a temperature-controlled instrument room of the KPNO 2.1 m Coude room with yearly temperature variation within 2C to further reduce the instrument long term temperature variation.

EXPERT-III adopts a white pupil design, which enables a compact instrument and allows effective management of scattered light.  EXPERT-III is fed with three 80 m diameter fibers from the telescope (2.0 arcsec on sky and two science fibers) at f/4. One of the science fibers is coupled into four 40 m fibers. The outputs of the four fibers are arranged in a fiber slit head and re-imaged by relay optics to form f/10.2 beams which pass through the spectrograph entrance slit. This configuration allows the instrument to reach R~100,000 in the operating wavelengths  to form the EHR mode. An optical mode scrambler is used in the science fiber inside the chamber. This EHR mode is designed to reach extremely high precision RV measurements (~1 m/s or better) of stars with V~8 in 15 min exposures. The other science fiber and the sky fiber are also re-imaged by the relay optics and both beams are fed into the spectrograph to produce R~50,000 spectra to form the HR mode. This mode is designed for general spectroscopic observations and also high Doppler precision measurements of relatively faint stars with V>9. The sky fiber will produce sky background spectra for sky subtraction of stellar spectra obtained with the HR mode. A mask on a motor controlled slide is used for selecting which mode to observe. The table below summarizes EXPERT-III instrument parameters.

Wavelength region

0.38-0.9 m

Focal plane

4096x4096 Fairchild

Pixel size

15 m

Detector QE

~92% 0.38-0.65 m

~85% 0.65-0.75 m

77% at 0.8 m

54% at 0.9 m

Spectral resolution

R=100K (EHR mode)

R=50K (HR mode)

Dispersion per pix

0.017/pix at 0.55 m

Sampling

3 pixels (HR mode uses 2x2 binning)

Fiber diameter

2.0 arcsec (80 m)

Spectral orders

68-161 (0.38-0.90 m)

Single exposure coverage

5000

Design type

White pupil + refractive camera

Collimated beam

98 mm in diameter

Main dispersers

R4, 31.6 l/mm, 76 blaze

Cross-dispersers

(prisms)

PBM18Y prisms with 46 and 50 apex angles

Optical bench

1.34x0.8x0.48 meter

The following figure shows a solar spectrum taken with the EHR mode in EXPERT-III in a UF lab. The 4kx4k CCD detector covers 0.38-0.90 m in a single exposure.

 

The following figure shows part of a reduced solar spectrum around ~562 nm and its comparison with a simulated R=120K solar spectrum. Both spectra show quite similar spectral profiles, indicating similar spectral resolution.

Back to Top

 

Silicon Immersion Grating Technology Back

Silicon immersion diffraction gratings fabricated by photolithography and anisotropic chemical etching techniques being developed by an interdisciplinary team led by Jian Ge will be key dispersing elements for next generation space and ground-based IR spectroscopic instruments. Due to its very high refractive index (n = 3.4 at 2.2 micron), a silicon immersion grating can provide more than three times dispersion of a conventional reflective grating of equal length. Therefore, silicon immersion gratings will enable very compact IR spectroscopic instruments while provide high dispersion power.

We have successfully developed the world's first silicon grisms in 1999. They have 10x10 mm2 etched grating area and 46 deg wedge angles as shown in the following figure. The key team members include Jian Ge, and senior engineers, Dino Ciarlo and Paul Kuzmenko. The first light of one of the grisms at the Lick 3m telescope with the IRCAL near-IR camera and adaptive optics has demonstrated a diffraction-limited spectral resolution, R = 5,000 at 2.2 micron with a pupil diameter of only 5 mm. This spectral resolution is the highest ever obtained with grisms. The measured total grating efficiency is 36% and the integrated scattered light level from the grism is about 30%. Coupled with the Lick AO system, it allows efficient IR spectroscopy at very high spatial resolution at 0.2 arcsec. Combined with a conventionally made CaF2 grism cross-disperser, it allows a complete wavelength coverage in the K band.

 

 

In 1999, we (Prof. Ge, D. Ciarlo and P. Kuzmenko (LLNL)) developed a another technique which reduces grating surface roughness from the original rms 50 nm to 20 nm, which has reduced the total integrated scattered level to about 8% in the K band. A new set of the grisms has been used for scientific observations of T Tauri stars and Ae/Be stars and their companions at the Lick 3m in September 2000. The total grating efficiency has been increased to 45%.

The silicon immersion gratings promise a major impact in IR spectroscopy. The silicon grisms promise a very convenient and inexpensive way to implement intermediate and high spectral resolution in any existing IR camera. The silicon immersion gratings offer high efficiency and very high spectral resolving power (R > 100,000) in the IR for the first time.

Prof. Ge's Penn State group (Prof. Ge, S. Miller, D. McDavitt, J. Bernecker, A. Chakraborty, J. Wang and J. Friedman) has developed new etching processes based on TMAH instead of previous KOH for fabricating silicon grisms and immersion gratings, taking advantage of state-of-the-art nanofabrication facility, Nanofab, at Penn State. The rms grating surface roughness has been reduced to ~ 3 nm and the intergrated scattered light level is less than 1%. This new technique has been used for fabricating new generations of silicon grisms and also silicon immersion gratings with up to 4 inch etched grating size. These grisms will be used in the NGST prototype near-IR multi-object spectrograph led by Dr. Harvey Moseley at GSFC, the FLAMINGOS near-IR MOS led by Dr. Richard Elston at University of Florida and PISCES near-IR wide field camera and Arizona Imager and Echelle Spectrograph (ARIES) led by Dr. Don McCarthy at Steward Observatory.

 

 

Several silicon immersion gratings are being developed at Penn State and used in the Arizona IR Imager and Echelle Spectrograph (ARIES) at the MMT 6.5m. A silicon immersion grating with 2 inch pupil diameter will provide R = 120,000 in 1.2-5.5 micron. The main science goal for such high resolution spectroscopy is to detect emission lines of CO fundamental band at 4.6 micron caused by the residual gas in the dynamic gaps caused by the young planets. The high resolution spectroscopy allows us to study the location, total mass of the planets, density and temperature of the residual gas with the planet formation. The very low thermal emissivity of the MMT 6.5m adaptive optics provide great sensitivity for this exciting study. Back to Top

 

Michelson Type Fixed-delay Interferometers     Back

A prototype dispersed fixed-delay interferometer has been developed at Penn State by Prof. Ge's team, including J. van Eyken, S. Mahadevan, C. DeWitt, J. Liu, Prof. J. Ge and Dr. S. Shaklan (JPL), collaborated with Mike Rushford at LLNL, and has been used at the HET 9m and Palomar 5 m telescopes in 2001. It was used again at the KPNO 2.1m telescope in 2002 and routinely provided observations of stars as faint as V = 7.6. The total instrument throughput from the sky to the detector is ~5% (excluding iodine absorption), comparable to or slightly higher than that for current echelle instruments. A new f/3 instrument is being developed at Penn State and will provide ~ 20% total throughput by using both interferometer outputs, volumn phase holographic grating and better designed optics. It will see first light at the KPNO 2.1m telescope in the summer 2003 and a long term survey for extrasolar planet will be launched shortly after the instrument commissioning.

 

 Students working in this project have been exposed to almost every aspects of the instrument development, from optical-mechanical design, optical system alignment, system integration, CCD camera system testing to data taking and analysis. Back to Top

To Group Home Page

To Jian Ge's Home Page.


    First created: March 2,2000; Last updated: Feb. 10, 2016