Publications

An Expanded View of Cost Imposition: Application to Personnel and Nondefense Policies

Authors: Joseph R. Schmitt & Andrew Keith
Published July 20, 2020

Cost imposition warfare is a two-sided affair. It is usually discussed in terms of military equipment: increasing the cost of an adversary’s capabilities (offensive cost imposition) or reducing the cost of our own (defensive cost imposition), but that is a narrow and simplistic view. More important is the cost burden per capability or use, and it extends beyond just military equipment. Personnel costs comprise 37% of global military spending, and nondefense spending comprises nearly 98% of the world’s economy. In this paper, we broadened the idea of cost imposition to examine military personnel, immigration, health care, and alliances. We found that immigration could have especially large effects on future U.S. national power. In our simplified model projected to 2100, a zero migration model reduced potential annual defense spending by about $713 billion in FY2020 dollars, while doubling immigration increased potential annual defense spending by about $1 trillion. We also found that national health care reform could significantly reduce the cost burden of defense spending on a much shorter timescale. Reducing U.S. health care costs to the average level of other developed countries could free roughly $50 billion annually for defense if the savings were redistributed proportionally across national spending categories. More broadly, we argued that cost imposition should include policies well beyond weapons procurement because immigration, health care, military personnel policy, and alliances can all affect the relative cost of maintaining national power.

Links: Wild Blue Yonder and PDF.

A Search for Lost Planets in the Kepler Multi-planet Systems and the Discovery of the Long-period, Neptune-sized Exoplanet Kepler-150 f

Authors: Joseph R. Schmitt, Jon M. Jenkins, and Debra A. Fischer
Published March 28, 2017

The Kepler space telescope has discovered thousands of planets, including many stars with multiple planets. In systems with many planets, long-period planets can be especially hard to detect because their signals are easily obscured by those of the other planets. In this paper, I examined stars with three or more known planets, modeled their orbits, and removed their signals. Hidden in the remaining noise, I discovered a new signal. Using a variety of statistical techniques, I confirmed it as the exoplanet Kepler-150 f, the fifth known planet in the system. Kepler-150 f is approximately the size of Neptune and orbits its star in the habitable zone once every 637 days. It lies about 3,000 light-years from Earth.

Links: The Astronomical Journal, ADS, arXiv, PDF, and PDF (small).

Sample news coverage: Yale News, Astronomy.com, Gizmodo, and The Indian Express.

Planet Hunters. X. Searching for Nearby Neighbors of 75 Planet and Eclipsing Binary Candidates from the K2 Kepler Extended Mission

Authors: Joseph R. Schmitt and 24 others
Published May 27, 2016

In this paper, we observed 75 stars believed either to host planets or to be closely orbiting pairs of stars. Target stars were selected exclusively by volunteers from the citizen science project Planet Hunters. This crowd-sourcing project allows users online to examine real Kepler data and conduct their own searches for exoplanets and other interesting phenomena. Among the 75 target stars, 10 are newly discovered hosts to planet candidates. These are likely to be true planets but have not quite met the high statistical standard required to be declared confirmed. We used two telescopes, the Southern Astrophysical Research (SOAR) telescope in Chile and the Keck II telescope in Hawaii, to perform high-resolution imaging of our target stars. Our observations found that at least 9 of the 75 stars had a neighboring star in their vicinity, including 6 newly discovered companions and one around a planet candidate host star. These high-resolution observations will be useful for future planet vetting and for studies of the frequency of nearby stars in planetary and eclipsing-binary systems.

Links: The Astronomical Journal, ADS, arXiv, and PDF.

Modeling the Asteroseismic Surface Term Across the HR Diagram

Authors: Joseph R. Schmitt and Sarbani Basu
Published July 27, 2015

Astronomers have historically struggled to accurately and precisely measure the masses, radii, ages, and other important properties of many stars. Asteroseismology is a powerful tool that helps overcome this problem by measuring the frequencies at which stars pulsate. In theory, these measured frequencies can be matched to the pulsation frequencies of computer models of stars, allowing astronomers to compare a real star with unknown properties to a model star with known properties and infer the real star’s characteristics. However, imperfections in how stellar surfaces are modeled produce errors known as the “surface term,” which must be corrected to obtain accurate stellar properties. In this paper, we created computer simulations of the surface term for stars spanning a wide range of properties and ages to determine how best to correct for it. We found that the correction model proposed by Ball & Gizon (2014) performed much better than the other models we tested for nearly all of the simulated stars in our study. Based on these results, we recommended the Ball & Gizon (2014) model for future asteroseismic analyses.

Links: The Astrophysical Journal, ADS, arXiv, and PDF.

Planet Hunters. VII. Discovery of a New Low-mass, Low-density Planet (PH3 c) Orbiting Kepler-289 with Mass Measurements of Two Additional Planets (PH3 b and d)

Authors: Joseph R. Schmitt and 20 others
Published October 28, 2014

The Kepler space telescope stared at more than 150,000 stars for four straight years looking for the rare moments when an exoplanet, a planet beyond our solar system, crossed in front of its star. Most planets have highly regular orbits and transit at nearly the same time every orbit. However, when multiple planets orbit the same star, their gravitational interactions can cause those transit times to shift. Planet Hunters, a citizen science project where online volunteers examine real Kepler data to help find exoplanets, identified such a case in the PH3 (or Kepler-289) system, which already had two known planets. A Planet Hunters user found an additional signal whose transit times changed by as much as 10 hours over the course of just a few orbits, a staggering amount. These variations allowed us to measure the planet’s mass at about 4.0 times the mass of Earth, confirming the signal as a planet called PH3 c. With a radius 2.7 times that of Earth, PH3 c has a substantial atmosphere of hydrogen and helium, unusual for a planet of such low mass. PH3 c joined a newly recognized class of low-mass, low-density planets whose formation and evolution are not yet fully understood.

Links: The Astrophysical Journal, ADS, arXiv, and PDF.

Sample news coverage: Yale News, Astronomy.com, and Sci-News.

Planet Hunters. VI. An Independent Characterization of KOI-351 and Several Long Period Planet Candidates from the Kepler Archival Data

Authors: Joseph R. Schmitt and 32 others
Published June 26, 2014

NASA’s Kepler space telescope discovered thousands of planets, mostly with the aid of complex computer algorithms. However, some planets can escape those searches, especially planets with long orbital periods, planets in systems with many other planets, or planets whose transits do not occur at perfectly regular intervals. Planet Hunters is a citizen science project designed to help find these missed planets by showing real Kepler data to volunteers online and asking them to look for the characteristic dip in a star’s brightness as a planet crosses in front of it. With their help, we discovered 14 new planet candidates that the automated searches had missed, including many with very long orbital periods. Half of the new planet candidates orbit in their host stars’ habitable zones. One of the 14 candidates resides in the KOI-351 system, which already had six known planet candidates. The newly identified candidate had both a relatively long orbital period and extremely large transit timing variations, at one point appearing 24 hours later than expected because of gravitational interactions with the other planets in the system. At the time, our discovery brought KOI-351 to seven known planet candidates, the most then known around any star outside our solar system. The system, now called Kepler-90, has since been shown to contain eight confirmed planets, tying our solar system for the largest known number of planets orbiting a single star.

Links: The Astronomical Journal, ADS, arXiv, and PDF.

Sample news coverage: BBC and Sky and Telescope.

Calibrating Iodine Cells for Precise Radial Velocities

Authors: Sharon Xuesong Wang and 6 others, including Joseph R. Schmitt
Published December 6, 2019

One of the most effective methods for discovering exoplanets is the radial velocity technique, also called the Doppler method or the “wobble technique”. This method relies on the fact that gravity works in both directions: the planet feels the gravitational pull of the star, and the star feels the gravitational pull of the planet. As a result, both orbit their common center of mass, although the star moves much less because it is far more massive. That motion can be detected by observing a star’s spectrum, which shows how much light the star emits at different wavelengths. Elements in the star’s atmosphere absorb specific wavelengths, imprinting a unique pattern of absorption lines on the spectrum. As the star moves back and forth under the gravitational influence of its planets, those absorption lines shift with it. To measure that motion precisely and confirm an exoplanet’s existence, astronomers need a stable reference spectrum. One common method is to use a cell of gaseous iodine in the telescope’s light path, which imprints a known reference pattern on the stellar spectrum. That iodine reference is typically characterized using a Fourier Transform Spectrometer (FTS). In this work, we investigated why the iodine reference measured with our extremely high-resolution spectrograph differed from the FTS measurements. We concluded that the discrepancy was caused by differences in the temperature of the iodine cell. We also showed that extremely high-resolution spectrographs can be used to validate FTS measurements and diagnose deficiencies in them.

Links: Publications of the Astronomical Society of the Pacific, ADS, and arXiv.

Planet Hunters IX. KIC 8462852 - Where's the Flux?

Authors: Tabetha S. Boyajian and 48 others, including Joseph R. Schmitt
Published January 27, 2016

Called “The Most Mysterious Star in the Galaxy” by The Atlantic because of speculation that KIC 8462852 might host an “alien megastructure”, an idea explored in a separate follow-up paper, our original paper made no reference to aliens. Instead, our team, led by Dr. Tabetha Boyajian, explored a series of natural explanations for the star’s chaotic and unprecedented dips in brightness. At times, these dips block up to 40% of the star’s light. With no discernible pattern and no comparable example then known, we examined a variety of possible explanations, including a catastrophic collision between two planets, a series of collisions between large asteroids, a huge family of comets, and others. None of these scenarios provided a completely satisfactory explanation, but the most plausible of those we considered was a large family of comets whose massive comas could obscure varying amounts of the star’s light as they passed in front of it.

Links: Monthly Notices of the Royal Astronomical Society, ADS, arXiv, and PDF.

Sample news coverage: CNN, CBS News, NBC News, Newsweek, Bloomberg, and The Guardian.

Planet Hunters. VIII. Characterization of 41 Long-period Exoplanet Candidates from Kepler Archival Data

Authors: Ji Wang, Debra A. Fischer, Thomas Barclay, Alyssa Picard, Bo Ma, Brendan Bowler, Joseph R. Schmitt, and 26 others
Published December 18, 2015

The Kepler space telescope was the most prolific planet discoverer of its time. For four straight years, it stared at more than 150,000 stars in hopes of catching the slight dimming that occurs when a planet crosses in front of its star. These transits block a small fraction of the starlight, producing dips in brightness that Kepler could detect. Computer algorithms are very good at finding these signals when the transits repeat many times at regular intervals. They are much less effective when only one or two transits are visible, which often happens for planets with orbital periods comparable to or longer than Kepler’s four-year observing window. Long-period planets are especially interesting because some may reside in or beyond their stars’ habitable zones, where relatively few planets had been identified at the time. To help find these systems, the Planet Hunters citizen science project allowed volunteers online to search the Kepler data themselves. Planet Hunters users made the initial discoveries of 41 long-period planet candidates, most of which Dr. Wang later observed with the Keck II and Palomar 200-inch telescopes. Using statistical techniques, we showed that 7 of the 41 candidates were consistent with being bona fide planets at high confidence, making them valuable additions to the relatively small sample of known long-period exoplanets.

Links: The Astrophysical Journal, ADS, arXiv, and PDF.

Kepler eclipsing binary stars - VI. Identification of eclipsing binaries in the K2 Campaign 0 data set

Authors: Daryll M. LaCourse and 17 others, including Joseph R. Schmitt
Published August 5, 2015

After suffering a malfunction in one of its steering components, NASA’s Kepler space telescope began a new phase of its mission, K2, in which the telescope observed a different patch of sky about every three months. A group of amateur astronomers, led by Planet Hunter Daryll LaCourse, examined the first three months of K2 data to search for eclipsing binaries, pairs of stars orbiting each other in which one or both stars pass in front of the other and block some of their light. Characterizing eclipsing binary populations helps astronomers understand the environments in which stars form, and eclipsing binaries are also one of the most common false positives in exoplanet searches. Using techniques they had learned and developed through their work on the citizen science project Planet Hunters, the team found 207 eclipsing binaries, including 97 new discoveries. In a serendipitous result, the team also identified two exoplanet candidates. Daryll LaCourse later received the American Astronomical Society’s Chambliss Amateur Achievement Award for this study.

Links: Monthly Notices of the Royal Astronomical Society, ADS, arXiv, and PDF.

Planet Hunters. V. A Confirmed Jupiter-Size Planet in the Habitable Zone and 42 Planet Candidates from the Kepler Archive Data

Authors: Ji Wang and 21 others, including Joseph R. Schmitt
Published September 19, 2013\

Thousands of exoplanets, planets beyond our solar system, have been discovered so far. Most were found using NASA’s Kepler space telescope, which launched in 2009 and stared at the same patch of sky for four straight years looking for planets crossing in front of their host stars. These “transits” cause a star’s brightness to dip as the planet blocks some of its light. While computer algorithms are excellent at finding most of these planets, some are missed, especially planets with long orbital periods or planets whose transits do not occur at perfectly regular intervals. The Planet Hunters citizen science project is particularly good at finding these missed planets because volunteers can examine real Kepler data online and identify transit signals themselves. In this paper, Planet Hunters volunteers found 43 planet candidates and forwarded them to the science team for vetting. Dr. Wang led the team in confirming one of them, a Jupiter-sized exoplanet named PH2 b located in the habitable zone of its host star.

Links: The Astrophysical Journal, ADS, arXiv, and PDF.

Sample news coverage: Yale News, Space.com, The Independent, Universe Today, and Sci-News.

X-rays from Blue Compact Dwarf Galaxies

Authors: Philip Kaaret, Joseph Schmitt, and Mark Gorski
Published October 10, 2011

Blue compact dwarf galaxies are small galaxies containing many clusters of young, blue stars. These stars are massive, hot, and short-lived. Stars that are at least ~8 times more massive than the Sun live for only a few million to a few tens of millions of years before exploding as supernovae. The remnants of these explosions are usually neutron stars, extremely dense objects only a few miles across, or black holes, whose gravity is so strong that not even light can escape. If either object has a stellar companion, it can pull material away from that star. As this material falls toward the neutron star or black hole, it can become hot enough to emit X-rays, creating a system known as an X-ray binary. Because X-ray binaries tend to appear relatively soon after massive stars form and die, their number and total X-ray brightness can be used as a measure of recent star formation in a galaxy. In this study, Dr. Kaaret led our group in observing blue compact dwarf galaxies with the Chandra X-ray Observatory. We discovered several X-ray binaries and compared their number and brightness with other measurements of the galaxies’ star formation rates. We found that blue compact dwarfs contain more X-ray binaries and produce substantially more X-ray emission from them than typical galaxies with similar star formation rates. Because blue compact dwarf galaxies are thought to resemble some galaxies in the early universe, our results suggested that X-ray binaries may have played a larger role than previously thought in heating the early universe.

Links: The Astrophysical Journal, ADS, arXiv, and PDF.