About Me

Kevin K. Hardegree-Ullman

Kevin K. Hardegree-Ullman, Ph.D.

I explore exoplanets, cool stars, and brown dwarfs!

UA Logo

University of Arizona

I study exoplanets around cool stars with Dr. Dániel Apai!



Caltech Logo

Caltech

I explored exoplanet demographics at IPAC-NExScI with Dr. Jessie Christiansen!

UT Logo

University of Toledo

I completed my Ph.D. in Physics in 2018. I conducted exoplanet and brown dwarf research with Dr. Michael Cushing!

Research: Recent Highlights

Exoplanets  K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System

Kevin K. Hardegree-Ullman, et al. 2021. AJ 161, 219.

Synopsis: We confirm the existence of K2-138 g with Spitzer data. The 3.44 R planet orbits its host star every 41.97 days, so only two transits were identified in the original K2 data.

K2-138 g light curves from K2 (left) and Spitzer (right).

Stars   Exoplanets   Scaling K2. I. Revised Parameters for 222,088 K2 Stars and a K2 Planet Radius Valley at 1.9 R

Kevin K. Hardegree-Ullman, et al. 2020. ApJS, 247, 28.

Synopsis: We updated stellar parameters for 222,088 K2 stars (download table here 94MB). We applied the uniformly derived stellar parameters to 299 confirmed and 517 candidate K2 planets to refine their radii and incident stellar flux (download table here 190KB), elucidating a conclusive planet radius valley in a data set other than Kepler for the first time. The image below on the left shows the individual K2 planet radii versus their incident flux relative to Earth (points). The density contours are shown behind the points. The image on the right shows the K2 density contours compared to those from the Kepler mission planets (Fulton+ 2018). The planet radius valley is at the same location in both data sets, with hints of a small slope with respect to incident flux.

Kepler planet occurrence rates as a function of spectral type.

Stars   Exoplanets   Kepler Planet Occrrence Rates for Mid-type M Dwarfs as a Function of Spectral Type

Kevin K. Hardegree-Ullman, et al. 2019. AJ, 158, 75.

Synopsis: Using updated stellar parameters from spectra and parllaxes we computed planet occurrence rates for Kepler mid-type M dwarfs. The image below shows our revised occurrence rates compared to literature values for early-type M dwarfs and FGK dwarfs.

Kepler planet occurrence rates as a function of spectral type.

Stars   Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. IV. Updated Properties for 86 Cool Dwarfs Observed during Campaigns 1-17

Courtney D. Dressing, Kevin K. Hardegree-Ullman, et al. 2019. AJ, 158, 87.

Synopsis: We revised stellar properties for 172 K2 planet candidate host stars, 86 of which were cool dwarfs. The image below shows how the updated stellar parameters compare to those from the EPIC.

Changes from EPIC stellar properties.

Exoplanets   Catalog of New K2 Exoplanet Candidates from Citizen Scientists

Jon K. Zink, Kevin K. Hardegree-Ullman, et al. 2019. RNAAS, 3, 43.

Synopsis: We report 28 new K2 exoplanet candidates discovered by citizen scientists through the Exoplanet Explorers Zooniverse project. The (interactive!) plot below shows how the candidates compare to other K2 confirmed and candidate planets. Circle size indicates Kepler band magnitudes.

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Outreach

It's a beautiful day in the local stellar neighborhood!

We're all stuck at home, mostly limited to exploring our own boring neighborhoods. Why not explore the (more interesting) local stellar neighborhood with your very own model?! The following slides are a tutorial to make a scale model of the Sun and its closest neighbors out to 10 light years. For best readability, view slides in fullscreen.

Download and print the star cut out files here:

Black & white (color the stars yourself!)

Color

If you don't have a printer, you can use the table below for sizing. You can also make the stars bigger (I don't recommend smaller) by multiplying the star diameters by a number larger than 1.

Common Name Distance
(Light years)
Spectral Type Diameter Relative to Sun
(inches)
Diameter Relative to Sun
(cm)
Approximate Color x (inches) y (inches) z (inches) x (cm) y (cm) z (cm)
Sun 0.00 G2V 1.00 2.54 #FFF5F2 5.75 5.75 5.75 14.5 14.5 14.5
Proxima Centauri 4.24 M5.5V 0.15 0.39 #FFCC6F 4.75 5 8 12 12.5 20.5
Alpha Centauri A 4.37 G2V 1.22 3.11 #FFF5F2
Alpha Centauri B 4.37 K1V 0.86 2.19 #FFEEDD
Barnard’s Star 5.96 M4V 0.20 0.50 #FFC97F 5.75 2.25 5.5 14.5 5.5 14
Luhman 16 A 6.50 L8 0.11 0.28 #FF6060 3.5 6.5 8.75 9 16.5 22
Luhman 16 B 6.50 T1 0.11 0.28 #FF4080
WISE 0855-0714 7.26 Y2 0.11 0.28 #9366B4 3 8.75 6.25 7.5 22 16
Wolf 359 7.86 M6 0.16 0.41 #FFC370 1.5 7 5.25 4 18 13.5
Lalande 21185 8.31 M2 0.39 1.00 #FFC483 2 6.75 3 5 17 7.5
Sirius A 8.66 A1 1.71 4.35 #B5C7FF 4.75 10.5 7.25 12 26.5 18.5
Sirius B 8.66 DA2 0.01 0.02 #A8BDFF
Luyten 726-8 A 8.79 M5.5V 0.14 0.36 #FFCC6F 10 7.75 7.25 25.5 19.5 18.5
Luyten 726-8 B 8.79 M6V 0.14 0.36 #FFC370
Ross 154 9.70 M3.5V 0.24 0.61 #FFCE81 6.75 0.75 8 17 2 20.5

 
 

The Planet Coloring Book!

Color in the planets of the Solar System and the 55 closest confirmed planets orbiting other stars! Planet sizes are to scale, so you can see how the "exoplanets" compare to the ones we all know and love! Cut out and hang these planets anywhere, and you can even come up with your own (much more creative) planet names!

Download and print the coloring book here!



Multimedia

The Exoplanet R(E)volution. Virtual talk given on March 4, 2021 to Embry-Riddle Aeronautical University-Prescott as part of The Jim and Linda Lee Planetarium Science Speaker Series.

American Astronomical Society press release: Spitzer confirmation of K2-138 g.

Surely You're Joking podcast about the K2-138 exoplanet system.

Synopsis of my M dwarf research by Active Galactic Videos.

Outreach video to help explain gravity using a spandex gravity well.


Curriculum Vitae: Kevin K. Hardegree-Ullman

Postdoctoral Scholar - University of Arizona/Steward Observatory

Contact Information

933 N Cherry Ave
Tucson, AZ 85719

 

E-mail: ude.anozira@uhknivek
Website: kevinkhu.com

Education

Ph.D. Physics, The University of Toledo
2018
B.S. Astronomy, The University of Arizona
2011

Professional History

Postdoctoral Scholar, University of Arizona/Steward Observatory
2021-Present
Postdoctoral Scholar, Caltech/IPAC-NExScI
2018-2021
Visiting Graduate Fellow, IPAC
2017
Lead Observer, Ritter Observatory, University of Toledo
2013-2017

Mentoring History

Rachel Fernandes, Ph.D. Candidate, University of Arizona/LPL
2020-Present
Jon Zink, Ph.D. Candidate, University of California, Los Angeles
2019-Present

First/Second Author Publications

Exoplanets Scaling K2. IV. A Uniform Planet Sample for Campaigns 1-8 and 10-18
          Zink, J. K.; Hardegree-Ullman, K. K.; Christiansen, J. L.; et al. 2021. AJ Accepted.
Exoplanets K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System
          Hardegree-Ullman, K. K.; Christiansen, J. L.; Ciardi, D. R.; et al. 2021. AJ 161, 219.
Exoplanets Scaling K2. III. Comparable Planet Occurrence in the FGK Samples of Campaign 5 and Kepler
          Zink, J. K.; Hardegree-Ullman, K. K.; Christiansen, J. L.; et al. 2020. AJ, 160, 94.
Exoplanets Scaling K2. II. Assembly of a Fully Automated C5 Planet Candidate Catalog Using EDI-Vetter
          Zink, J. K.; Hardegree-Ullman, K. K.; Christiansen, J. L.; et al. 2020. AJ, 159, 154.
Stars Exoplanets Scaling K2. I. Revised Parameters for 222,088 K2 Stars and a K2 Planet Radius Valley at 1.9 R
          Hardegree-Ullman, K. K.; Zink, J. K.; Christiansen, J. L.; et al. 2020. ApJS, 247, 28.
Stars Exoplanets Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. IV. Updated Properties for 86 Cool Dwarfs Observed during Campaigns 1-17
          Dressing, C. D.; Hardegree-Ullman, K. K.; Schlieder, J. E. et al. 2019. AJ, 158, 87.
Exoplanets Catalog of New K2 Exoplanet Candidates from Citizen Scientists
          Zink, J. K.; Hardegree-Ullman, K. K.; Christiansen, J. L. et al. 2019. RNAAS, 3, 43.
Stars Exoplanets Kepler Planet Occurrence Rates for Mid-type M Dwarfs as a Function of Spectral Type
          Hardegree-Ullman, K. K.; Cushing, M. C.; Muirhead, P. S.; Christiansen, J. L. 2019. AJ, 158, 75.
Brown Dwarfs  Spitzer Light Curves of the Young, Planetary-Mass TW Hya Members 2MASS J11193254-1137466AB and WISEA J114724.10-204021.3
          Schneider, A. C.; Hardegree-Ullman, K. K.; Cushing, M. C.; et al. 2018. AJ, 155, 238.
Brown Dwarfs  The First Detection of Photometric Variability in a Y Dwarf: WISE J140518.39+553421.3
          Cushing, M. C.; Hardegree-Ullman, K. K.; Trucks, J. L. et al. 2016. ApJ, 823, 152.
A New Online Astronomy Resource for Education and Outreach
          Impey C. D.; Hardegree-Ullman, K. K. Patikkal, A. et al. 2013. Astro. Ed. Rev., 12, 010301

Co-Author Publications

Exoplanets WASP-107b's Density Is Even Lower: A Case Study for the Physics of Planetary Gas Envelope Accretion and Orbital Migration
          Piaulet, C.; Benneke, B.; Rubenzahl R. A. et al. 2021. AJ, 161, 70.
Exoplanets Transmission spectroscopy for the warm sub-Neptune HD3167c: evidence for molecular absorption and a possible high metallicity atmosphere
          Mikal-Evans, T.; Crossfield, I. J. M.; Benneke, B. et al. 2021. AJ, 161, 18.
Exoplanets Tentative Evidence for Water Vapor in the Atmosphere of the Neptune-Size Exoplanet HD 106315 c
          Kreidberg, L.; Mollière, P.; Crossfield, I. J. M. et al. 2020. AJ Submitted.
Exoplanets Revisiting the HIP 41378 System with K2 and Spitzer
          Berardo, D.; Crossfield, I. J. M.; Werner, M. et al. 2019. AJ, 157, 185.
Exoplanets Bright Opportunities for Atmospheric Characterization of Small Planets: Masses and Radii of K2-3 b, c, and d and GJ3470 b from Radial Velocity Measurements and Spitzer Transits
          Kosiarek, M. R.; Crossfield, I. J. M.; Hardegree-Ullman, K. K.; et al. 2019. AJ, 157, 97.
Exoplanets Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars III: A High Mass & Low Envelope Fraction for the Warm Neptune K2-55b
          Dressing, C. D.; Sinukoff, E.; Fulton, B. J. et al. 2018. AJ, 156, 70.
Exoplanets Planetary Candidates from K2 Campaign 16
          Yu, L.; Crossfield, I. J. M.; Schlieder, J, E. et al. 2018. AJ, 156, 22.
Stars Brown Dwarfs  2MASS J11151597+1937266: A Young, Dusty, Isolated, Planetary-Mass Object with a Potential Wide Stellar Companion
          Theissen, C. A.; Burgasser, A. J.; Bardalez Gagliuffi, D. C.; et al. 2018. ApJ, 853, 75.
Exoplanets Investigating the Physical Properties of Transiting Hot Jupiters with the 1.5-m Kuiper Telescope
          Turner, J. D.; Leiter, R. M.; Biddle, L. I.; et al. 2017. MNRAS, 472, 3871.
Stars The Most Massive Heartbeat: An In-Depth Analysis of Iota Orionis
          Pablo, H.; Richardson; N. D.; Fuller, J. et al. 2017. MNRAS, 467, 2494.
Stars A Spectroscopic Orbit for the Late-type Be Star Beta CMi
          Dulaney, N. A.; Richardson, N. D.; Gerhartz, C. J. et al. 2017. ApJ, 836, 112.
Brown Dwarfs  Photometric Monitoring of the Coldest Known Brown Dwarf with the Spitzer Space Telescope
          Esplin, T. L.; Luhman, K. L.; Cushing, M. C.; et al. 2016. ApJ, 832, 58.
Brown Dwarfs  Observed Variability at 1μm and 4μm in the Y0 Brown Dwarf WISEP J173835.52+273258.9
          Leggett, S. K.; Cushing, M. C.; Hardegree-Ullman, K. K.; et al. 2016. ApJ, 830, 141.
Exoplanets Ground-Based Near-UV Observations of 15 Transiting Exoplanets: Constraints on Their Atmospheres and No Evidence for Asymmetrical Transits
          Turner, J. D.; Pearson, K. A.; Biddle, L. I.; et al. 2016. MNRAS, 459, 789.
Exoplanets Near-UV and Optical Observations of the Transiting Exoplanet TrES-3b
          Turner, J. D.; Smart, B. M.; Hardegree-Ullman, K. K.; et al., 2013. MNRAS, 428, 678.

Awards and Grants

NASA WIYN PI Data Awards: $109,400
2015-2018
          NASA/NSF Exoplanet Exploration Program awards to characterize M dwarfs for Kepler and TESS exoplanet demographics studies using the WIYN telescope.
University of Toledo Graduate Student Association Award: $1,720
2014
          Award to construct a flat field calibration system for Ritter Observatory.

Telescope Time as PI

SOAR - NOIRLab Survey Program
2019-Present
          Atmospheric survey of giant exoplanets observed or discovered by TESS.
30 nights
2016-2020
          Kepler M dwarfs and optical/IR metallicity calibration projects.
17 nights
2015-2018
          Kepler M dwarfs and TESS cool star characterization projects.
46 nights
2013-2017
          Kepler M dwarfs and transiting exoplanet projects.
20 nights

Service

ExoPAG SAG #22 - Existing Stellar Catalogs Task Force Co-Lead
2020-Present
SOAR Telescope Science Advisory Committee
2020-Present

TESS Review Panelist
2020-2021

Referee for AAS Journals and MNRAS
2018-Present


Astrophotography

This is a collection of astronomical images I've taken recently at Ritter Observatory, the Lowell Discovery Telescope, and other areas of Arizona and Ohio. Please contact me if you want a full-resolution version or if you would like to use any of these images for any purpose.

M1 - Crab Nebula

M1 - Crab Nebula

Ritter Observatory

M13 - Hercules Cluster

M13 - Hercules Cluster

Ritter Observatory

M16 - Eagle Nebula

M16 - Eagle Nebula

Ritter Observatory

M27 - Dumbbell Nebula

M27 - Dumbbell Nebula

Ritter Observatory

M42 - Orion Nebula

M42 - Orion Nebula

Ritter Observatory

M57 - Ring Nebula

M57 - Ring Nebula

Ritter Observatory

M82 - Cigar Galaxy with SN2014J

M82 - Cigar Galaxy with SN2014J

Ritter Observatory

Horsehead Nebula

Horsehead Nebula

Discovery Channel Telescope

Pointing to the center of the Milky Way

Pointing to the center of the Milky Way

Near Assumption, Ohio

Camelopardalid Meteor Shower

Camelopardalid Meteor Shower

Near Assumption, Ohio

Observing at the LDT

Observing at the LDT

Lowell Discovery Telescope

Annular Eclipse

Annular Eclipse

Horseshoe Bend, Arizona - May 20, 2012

Venus Transit - Mt. Lemmon SkyCenter, Arizona - June 5, 2012