Michael Bottom


My research is generally focused on exoplanet detection and characterization.  I am interested in using new technologies to develop more sensitive and effective instruments towards that goal.  I do most of my work at Caltech, the Jet Propulsion Lab, and at various observatories around the world including Keck, Palomar, and NASA's Infrared Telescope Facility.

Current Projects

Minerva
Radial velocity detection of low-mass exoplanets is a challenging task, both due to the high precision required and large amount of observing time necessary for dense orbital phase coverage.

Minerva (MINiature Exoplanet Radial Velocity Array) tackles these two issues simultaneously, using four automated 0.7 m telescopes fiber-feeding the same high-resolution spectrograph.  It is designed for  high-cadence, high-precision radial velocity searches for extrasolar planets orbiting nearby stars, with additional photometric capabilities. Its final location is Mt. Hopkins observatory in Arizona, but the telescope, enclosure, and related hardware are currently being tested and configured here in Pasadena.

minerva_caltech  fiber_coupled  wasp_12b
(Left) The test facility at Caltech, with the first telescope visible. (Center) Coupling starlight into the optical fiber.
(Right) Observing a transiting exoplanet (from Pasadena!
)

I work primarily on the implementation of the telescope system--ie, the hardware and software.  I also performed an end-to-end simulation of the optimal design of a Minerva-like survey, the results of which were published here.

For more information, visit the group web site.

Direct imaging of planets with a multistage vortex coronagraph
High contrast imaging is the most promising way of studying planets at intermediate to large separations from their host stars.  Discovery of these planets is necessary in order to understand exoplanet population statistics, exoplanet chemistry, the formation and migration mechanisms of planetary systems, and their relationship to dust structures.  However, direct imaging of planets is currently limited both by achievable contrast and by the inner working angle, which limit how faint and close-in companions can be detected.  To make progress in these areas, we are developing a new coronagraph at JPL, the “Stellar Double Coronagraph” (SDC).  Unlike conventional coronagraphs, this uses a device called an optical vortex,  capable of reaching high contrast (10-6 – 10-7) at very small angles (~70 mas at H-band), or 0.9 λ/D , from the ground.  This will allow imaging of young, sub-Jupiter mass planets at ~AU separations around nearby stars, which are predicted to be much more common than currently imaged planets.


High precision near-infrared radial velocities
The near-infrared (NIR) bands are a promising but difficult place to do high-precision Doppler spectroscopy.  Small stars, which emit most of their flux in the NIR, have much higher reflex velocities from habitable-zone planets, making them excellent targets for radial-velocity surveys.  However, until recently, the instrumental stability and referencing that have resulted in successful visible-light instruments have simply not existed in the infrared.

A prototype high-precision radial velocity system has been under development at the NASA Infrared Telescope Facility (IRTF).  An isotopic methane cell is used as a wavelength reference, and a fiber optic scrambling system is used to produce a highly stable output illumination pattern.
 
fiber_scramblerfiber_vs_nofiber
(Left) The fiber scrambler disconnected from the telescope, with the fibers visible to the right.
(Right) A large improvement in RV precision can be seen when the fiber scrambler is in for S/N<350


I worked on the design, construction, and testing  of the fiber optic scrambler, and participated in the commissioning run at IRTF.  I am currently involved in the  observing program, where we are pushing the limits of the instrument's performance, down to the few m/s level.

I will be leading a paper on this once all the data has been analyzed, but an SPIE paper with preliminary results may be found here (preprint here).


Past Projects

Spectral characterization of M dwarfs
M dwarfs are the most common stars in the universe, and also the longest-lived: typically, they have main-sequence lifetimes dozens to hundreds of times the current age of the universe.  The fact that they have not yet had time to evolve off of the main sequence provides a unique opportunity for characterization, as metallicity is no longer degenerate with age.

fig2_from_PBJ
Normalized stellar intensity as a function of wavelength in a region sensitive to absolute
magnitude, with each line corresponding to bin-averaged spectra of width 0.1 magnitudes.
(Colors correspond to absolute Ks-band magnitude in the range 4.5 to 7.5.)


Sebastian Pineda, John Johnson and I developed a method of deducing the physical properties (mass, metallicity, absolute magnitude, etc) of M dwarfs using high-resolution spectroscopy.  We combined over 15 years' worth of Keck spectra to create high signal-to-noise spectra of ~150 M dwarfs. We determined areas of the spectra sensitive to the fundamental properties of these stars, and then used  spectral indices to determine these properties for uncharacterized M dwarfs.

A link to the paper can be found here.

LAEDI
LAEDI (Lock-in Amplified Externally Dispersed Interferometer) is a novel testbed instrument built to achieve an unprecedented 10 cm/s of velocity precision on celestial objects, small enough to detect the p-mode oscillations on the Sun, or even the tug of the Earth. It will point the way towards extreme-precision instruments on the next generation of telescopes, capable of detecting habitable planets around Sun-like stars.

I assisted with the construction and testing of the hardware, particularly towards the goal of interfacing LAEDI as an instrument on the Palomar 200-inch telescope, fed by its highly advanced P3K adaptive-optics system.

Fourier transform spectroscopy of microwave filters

Before coming to graduate school, I worked in Amber Miller's CMB lab, manufacturing and testing microwave filters for use in CMB experiments.  A large fraction of this time was spent building a Fourier transform spectrometer (FTS) to test these filters.  While I don't currently do research in CMB physics, this experience taught me a great deal about optics, electronics, and cryogenics, and motivated me to pursue a career in experimental astrophysics.