Ultraviolet Spectroscopy

Launch pad

I am the Project Scientist for the Cosmic Origins Spectrograph (COS), a sensitive UV spectrograph that was installed on the Hubble Space Telescope in 2009. COS has been in science operations since September 2009. During that time, it has observed the atmospheres of transiting exoplanets, probed accretion and outflows on stellar and galactic scales, and increased the observed path length through the local intergalactic medium by more than an order of magnitude. As of February 2016, there are 314 published papers in the literature using COS data.

Cosmic Origins Spectrograph CU page

Review talk from the HST3 Conference, October 2010

Interview about COS science
A HubbleSite video about calibrating HST's new instruments and early release science

Optical Spectroscopy

I am the Project Manager (and currently the stand-in Systems Engineer) for a conceptual design study for the GMACS instrument on the Giant Magellan Telescope. GMACS will be a multi-object optical spectrograph for GMT and is expected to be available at or near telescope first light in the early 2020s. GMACS will be able to observe simultaneously hundreds of objects as faint as 25th-26th mag over 350 1000nm at moderate resolving power (R≈1000-6000); additional operational imaging and spectroscopic modes will also be available to maximize operational and scientific flexibility. GMACS on GMT will have the highest product of effective telescope collecting area and solid angle field-of-view (A-Ω product) of any planned spectrograph for extremely large telescopes (up to 45 square arcminutes in some modes). Furthermore, we will maintain the ability for the instrument to interface with the planned MANIFEST fiber feed, which will ultimately allow use of large numbers of positionable fibers over the full ~300 square arcminute field of the GMT. GMACS is expected to be a workhorse instrument for GMT with science drivers ranging from stellar and exoplanet project to observational cosmology at high redshift. GMACS will also act as a key southern hemisphere capability for spectroscopic follow-up of LSST targets.

GMACS assembly

The current GMACS concept is a two-arm spectrograph with a slit mask at the focal plane providing the MOS capability. The VPH gratings and camera assemblies can rotate independently of each other (90° range of motion). Masks are exchanged using a cassette system at the top of the instrument.

Previous Projects

: I was the PI of a conceptual design study for a high resolution optical spectrograph for Gemini, GHOS (Froning et al. 2013). In a partnership with Ball Aerospace, Arizona State University, and the Labatorio Nacional de Astroficia in Brazil, we developed a conceptual design for a Cassegrain-mounted GHOS with predicted instrument efficiencies twice those of current comparable instruments on large aperture telescopes. We developed a full end-to-end integrated model of the instrument to fully characterize bench deformations under thermal, gravitational, and vibrational stimuli. This model allowed us to develop a bench design that was passively stable to ~8-30 micron deformation in a 1 hour exposure. The remaining correction to obtain the required image stability is achieved using active flexure control by actuating the focal plane arrays using precision hexapods. 

The left figure shows the strucutral finite element model of the GHOS bench and its deformation under 1G gravity load. The right figure is an isometric view of GHOS mounted to the Gemini Instrument Support Structure.

Finite element model deformation analysis.           Isometric view of the CU-GHOS conceptual design

This figure shows the predicted efficiency of CU-GHOS (in black) compared to current instruments: Magellan MIKE (blue), Keck HIRES (red), VLT UVES (purple), and Subaru HRS (green):

Predicted efficiency for CU-GHOS compared to current instruments.

: I was also the PI for a CU conceptual design study for HROS, a high-resolution optical spectrograph concept for the Thirty Meter Telescope project (Froning et al. 2006; Osterman et al. 2006). We developed a novel concept for high resolution optical spectroscopy on large aperture telescopes by replacing the canonical cross-dispersed spectrograph with a  dichroic tree to spectrally separate the light, feeding a bank of replicated 1st order spectrographs.  I am currently pursuing bench tests to demonstrate the feasibility of the dichroic tree, with the long-term goal of developing a design for a single-target or multi-object high resolution spectrograph for the next generation of extremely large telescopes.

Another project that sprang out of this study was an interest in precision spectroscopy. I am part of an effort, lead by Steven Osterman and Scott Diddams at NIST/Boulder, to develop optical and NIR astronomical laser combs to support radial velocity planet searches. The first NIR laser combwas successfully deployed at the Hobby Eberley Telescop (HET) in the summer of 2010. A facility NIR laser comb to support the Habitable Zone Planet Finder instrument for the HET has been funded by the NSF and is currently being developed.

The figures below illustrate the CU-HROS concept:

CU-HROS concept    CU-HROS


Thirty Meter Telescope

SPIE Summary of CU-HROS concept

Near-Infrared Imaging and Spectroscopy

In 2003 – 2005, I participated in construction and commissioning of NIC-FPS and NIR imager and Fabry-Perot spectrograph for Apache Point Observatory. 


As a graduate student, I participated in the construction and commissioning of CoolSpec, a NIR spectrograph for McDonald Observatory.