Eric L. N. Jensen

Swarthmore College, Swarthmore, Pennsylvania, United States

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Publications (64)195.74 Total impact

  • R. L. Akeson, E. L. N. Jensen
    The Astrophysical Journal 09/2014; 793(2):142. · 6.73 Impact Factor
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    Eric L N Jensen, Rachel Akeson
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    ABSTRACT: Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our Solar System; their orbits may be eccentric or inclined with respect to the host star's equator, and the population of giant planets orbiting close to their host stars suggests appreciable orbital migration. There is at present no consensus on what produces such orbits. Theoretical explanations often invoke interactions with a binary companion star in an orbit that is inclined relative to the planet's orbital plane. Such mechanisms require significant mutual inclinations between the planetary and binary star orbital planes. The protoplanetary disks in a few young binaries are misaligned, but often the measurements of these misalignments are sensitive only to a small portion of the inner disk, and the three-dimensional misalignment of the bulk of the planet-forming disk mass has hitherto not been determined. Here we report that the protoplanetary disks in the young binary system HK Tauri are misaligned by 60 to 68 degrees, such that one or both of the disks are significantly inclined to the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits, and that these conditions are present at the time of planet formation, apparently because of the binary formation process.
    Nature 07/2014; 511(7511):567-569. · 38.60 Impact Factor
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    ABSTRACT: We present the results of 45 transit observations obtained for the transiting exoplanet HAT-P-32b. The transits have been observed using several telescopes mainly throughout the YETI (Young Exoplanet Transit Initiative) network. In 25 cases, complete transit light curves with a timing precision better than 1.4 min have been obtained. These light curves have been used to refine the system properties, namely inclination i, planet-to-star radius ratio Rp/Rs, and the ratio between the semimajor axis and the stellar radius a/Rs. First analyses by Hartman et al. suggests the existence of a second planet in the system, thus we tried to find an additional body using the transit timing variation (TTV) technique. Taking also the literature data points into account, we can explain all mid-transit times by refining the linear ephemeris by 21 ms. Thus, we can exclude TTV amplitudes of more than ̃1.5 min.
    05/2014; 441(1).
  • R. L. Akeson, E. L. N. Jensen
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    ABSTRACT: We have conducted a survey of 17 wide (> 100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and ten secondaries, with disk masses as low as $10^{-4} M_{\odot}$. We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of $F_{mm} \propto M_{\ast}^{1.5-2.0}$ to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.
    The Astrophysical Journal 02/2014; 784(1). · 6.73 Impact Factor
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    ABSTRACT: In the determination of the dimensions of celestial objects, it is important to confirm results through multiple independent methods. Asteroseismology can be employed to determine the stellar density based on the observed pulsation spectrum of a star for which a high quality light curve is available. This stellar density can be used in conjunction with evolutionary models to determine the mass and radius of the star. Alternatively, masses and radii can be determined for eclipsing binary stars based on well-known techniques if radial velocity data are available. We present masses and radii for the eclipsing binaries KIC 7821010 and KIC 9474969, which are targets that have great potential for seeking mass and radius confirmation through asteroseismological means. Stellar parameters for these systems were found using short cadence observations collected over the course of 25 months by the Kepler spacecraft as well as ground-based radial velocity and photometric data. Analyzing the eclipses and radial velocity data, we find mass and radius measurements accurate at the ~1% level. We compare our results with mass-radius relations from stellar evolutionary models. Finally, we compare our results with preliminary mass and radius measurements from asteroseismology. We acknowledge support from the National Science Foundation via the grant AST-1109928.
    01/2014;
  • Eric L. Jensen, R. L. Akeson
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    ABSTRACT: Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our solar system. Planets' orbits may be eccentric or significantly inclined with respect to the host star's equator, and the population of giant planets orbiting very close to their host stars suggests significant orbital migration. There is currently no consensus on what causes the migration and produces inclined or eccentric orbits. Theoretical explanations often invoke interactions with a binary companion star on an orbit that is inclined relative to the planet's orbital plane. Such mechanisms require significant mutual inclinations between planetary and binary star orbital planes, which until now have not been measured. Here we show that at least one of the protoplanetary disks in the young binary system HK Tau is significantly inclined to the binary orbital plane. Our ALMA observations of the molecular gas in the system show that both stars have protoplanetary disks in Keplerian rotation, the first time that disk rotation has been detected around both stars in a binary. The two disk planes are misaligned by roughly 60° from each other, so at least one of the disks is inclined 30° or more from the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits. The misalignment is present at the time of planet formation, and it is apparently a part of the binary formation process. Thus, binary companions may be important drivers of the diversity of orbits seen in extrasolar planets. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00150.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile.
    01/2014;
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    ABSTRACT: There have been previous hints that the transiting planet WASP-3 b is accompanied by a second planet in a nearby orbit, based on small deviations from strict periodicity of the observed transits. Here we present 17 precise radial velocity measurements and 32 transit light curves that were acquired between 2009 and 2011. These data were used to refine the parameters of the host star and transiting planet. This has resulted in reduced uncertainties for the radii and masses of the star and planet. The radial-velocity data and the transit times show no evidence for an additional planet in the system. Therefore, we have determined the upper limit on the mass of any hypothetical second planet, as a function of its orbital period.
    Astronomical Journal. 12/2013; 146(6).
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    ABSTRACT: We report the discovery of KELT-6b, a mildly-inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was confirmed using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V=10.38 host star (TYC 2532-556-1) is a mildly evolved, late-F star with T_eff=6102 \pm 43 K, log(g_*)=4.07_{-0.07}^{+0.04} and [Fe/H]=-0.28 \pm 0.04, with an inferred mass M_*=1.09 \pm 0.04 M_sun and radius R_*=1.58_{-0.09}^{+0.16} R_sun. The planetary companion has mass M_p=0.43 \pm 0.05 M_Jup, radius R_p=1.19_{-0.08}^{+0.13} R_Jup, surface gravity log(g_p)=2.86_{-0.08}^{+0.06}, and density rho_p=0.31_{-0.08}^{+0.07} g cm^{-3}. The planet is on an orbit with semimajor axis a=0.079 \pm 0.001 AU and eccentricity e=0.22_{-0.10}^{+0.12}, which is roughly consistent with circular, and has ephemeris of T_C(BJD_TDB)=2456347.79679 \pm 0.00036 and P=7.845631 \pm 0.000046 d. Equally plausible fits that employ empirical constraints on the host star parameters rather than isochrones yield a larger planet mass and radius by ~4-7%. KELT-6b has surface gravity and incident flux similar to HD 209458b, but orbits a host that is more metal poor than HD 209458b by ~0.3 dex. Thus, the KELT-6 system is a metal-poor analog of HD 209458, and offers the unique opportunity to perform a comparative measurement of two similar planets in similar environments around stars of very different metallicities. The precise radial velocity data also reveal an acceleration indicative of a longer-period third body in the system, although the companion is not detected in Keck adaptive optics images.
    08/2013;
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    ABSTRACT: The tables summarize the properties of stars in Trumpler 37. The positions, names in different publications, photometry, spectral classification and extinction, and the proper motions are given in tablea1. All values were determined in earlier publications. Tablea2 shows the radial velocity, equivalent widths for Hα and Lithium, mass accretion, x-ray luminosity, and T Tauri type, as well as the membership probability from proper motion. These values were also determined in earlier publications. The following columns of the membership probabilities using different data were determined by us. The last columns in tablea2 presents the membership probability determined by us from the measured values as well as the extinction, and stellar masses. If data from different literature are available, the more recent one is given. (2 data files).
    VizieR Online Data Catalog. 08/2013;
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    ABSTRACT: With an apparent cluster diameter of 1.5{\deg} and an age of ~4 Myr, Trumpler 37 is an ideal target for photometric monitoring of young stars as well as for the search of planetary transits, eclipsing binaries and other sources of variability. The YETI consortium has monitored Trumpler 37 throughout 2010 and 2011 to obtain a comprehensive view of variable phenomena in this region. In this first paper we present the cluster properties and membership determination as derived from an extensive investigation of the literature. We also compared the coordinate list to some YETI images. For 1872 stars we found literature data. Among them 774 have high probability of being member and 125 a medium probability. Based on infrared data we re-calculate a cluster extinction of 0.9-1.2 mag. We can confirm the age and distance to be 3-5 Myr and ~870 pc. Stellar masses are determined from theoretical models and the mass function is fitted with a power-law index of alpha=1.90 (0.1-0.4 M_sun) and alpha=1.12 (1-10 M_sun).
    Astronomische Nachrichten 05/2013; · 1.40 Impact Factor
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    ABSTRACT: The transit signature of exoplanets provides an avenue through which characterization of exoplanetary properties may be undertaken, such as studies of mean density, structure, and atmospheric composition. The Transit Ephemeris Refinement and Monitoring Survey is a program to expand the catalog of transiting planets around bright host stars by refining the orbits of known planets discovered with the radial velocity technique. Here we present results for the HD 38529 system. We determine fundamental properties of the host star through direct interferometric measurements of the radius and through spectroscopic analysis. We provide new radial velocity measurements that are used to improve the Keplerian solution for the two known planets, and we find no evidence for a previously postulated third planet. We also present 12 years of precision robotic photometry of HD 38529 that demonstrate the inner planet does not transit and the host star exhibits cyclic variations in seasonal mean brightness with a timescale of approximately six years.
    The Astrophysical Journal 04/2013; 768(2):155. · 6.73 Impact Factor
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    ABSTRACT: Photometric follow-up of planets discovered by the radial velocity technique have yielded known transiting extra-solar planets, especially for those with the brightest host stars (e.g., HD 209458b). The only limitation to photometric precision is determined by the chosen telescope/instrument and small uncertainties in the timing of the transit. We have conducted follow-up observations of numerous known exoplanets, such as HD 37605 and HD 6434, using the updated Transit Ephemeris Refinement and Monitoring Survey (TERMS) pipeline. We have calculated the transit ephemerides via optimal observing windows and are able to fully characterize the planetary system and possible transit. While the field of exoplanets has expanded to include characterization, these are typically limited to shorter period orbits. Our program extends characterization to a much more diverse range of planetary orbits both in terms of longer periods and higher eccentricities. In the case of a null detection, our photometry is used to place constraints on orbital and astrophysical parameters of the planet.
    01/2013;
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    ABSTRACT: We report the discovery of KELT-3b, a moderately inflated 1.41 M_J, 1.37 R_J hot Jupiter orbiting a V=9.8 late F star in a 2.703-day orbit. KELT-3b is the third transit discovery from the KELT survey, and is orbiting one of the 20 brightest known transiting planet host stars, making it a promising candidate for atmospheric characterization studies. The planet's inflated radius and high incident flux matches the trend between those two properties seen in other hot Jupiters. Preliminary analysis of the orbital evolution of KELT-3b suggests that the planet has likely always received a level of incident flux above the empirically identified threshold for inflation. Early work on KELT-North was supported by NASA Grant NNG04GO70G. Work by B.S.G., J.D.E., and T.G.B. was partially supported by NSF CAREER Grant AST-1056524. We acknowledge support from the Vanderbilt Initiative in Data-intensive Astrophysics (VIDA).
    01/2013;
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    ABSTRACT: We report the discovery of KELT-3b, a moderately inflated transiting hot Jupiter with a mass of 1.477 (-0.067, +0.066) M_J, and radius of 1.345 +/- 0.072 R_J, with an orbital period of 2.7033904 +/- 0.000010 days. The host star, KELT-3, is a V=9.8 late F star with M_* = 1.278 (-0.061, +0.063) M_sun, R_* = 1.472 (-0.067, +0.065) R_sun, T_eff = 6306 (-49, +50) K, log(g) = 4.209 (-0.031, +0.033), and [Fe/H] = 0.044 (-0.082, +0.080), and has a likely proper motion companion. KELT-3b is the third transiting exoplanet discovered by the KELT survey, and is orbiting one of the 20 brightest known transiting planet host stars, making it a promising candidate for detailed characterization studies. Although we infer that KELT-3 is significantly evolved, a preliminary analysis of the stellar and orbital evolution of the system suggests that the planet has likely always received a level of incident flux above the empirically-identified threshold for radius inflation suggested by Demory & Seager (2011).
    11/2012;
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    ABSTRACT: As part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS), we present new radial velocities and photometry of the HD 192263 system. Our analysis of the already available Keck-HIRES and CORALIE radial velocity measurements together with the five new Keck measurements we report in this paper results in improved orbital parameters for the system. We derive constraints on the size and phase location of the transit window for HD 192263b, a Jupiter-mass planet with a period of 24.3587 \pm 0.0022 days. We use 10 years of Automated Photoelectric Telescope (APT) photometry to analyze the stellar variability and search for planetary transits. We find continuing evidence of spot activity with periods near 23.4 days. The shape of the corresponding photometric variations changes over time, giving rise to not one but several Fourier peaks near this value. However, none of these frequencies coincides with the planet's orbital period and thus we find no evidence of star-planet interactions in the system. We attribute the ~23-day variability to stellar rotation. There are also indications of spot variations on longer (8 years) timescales. Finally, we use the photometric data to exclude transits for a planet with the predicted radius of 1.09 RJ, and as small as 0.79 RJ.
    The Astrophysical Journal 06/2012; 754(1). · 6.73 Impact Factor
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    ABSTRACT: We present the discovery of KELT-1b, the first transiting low-mass companion from the wide-field Kilodegree Extremely Little Telescope-North (KELT-North) survey. The V=10.7 primary is a mildly evolved, solar-metallicity, mid-F star. The companion is a low-mass brown dwarf or super-massive planet with mass of 27.23+/-0.50 MJ and radius of 1.110+0.037-0.024 RJ, on a very short period (P=1.21750007) circular orbit. KELT-1b receives a large amount of stellar insolation, with an equilibrium temperature assuming zero albedo and perfect redistribution of 2422 K. Upper limits on the secondary eclipse depth indicate that either the companion must have a non-zero albedo, or it must experience some energy redistribution. Comparison with standard evolutionary models for brown dwarfs suggests that the radius of KELT-1b is significantly inflated. Adaptive optics imaging reveals a candidate stellar companion to KELT-1, which is consistent with an M dwarf if bound. The projected spin-orbit alignment angle is consistent with zero stellar obliquity, and the vsini of the primary is consistent with tidal synchronization. Given the extreme parameters of the KELT-1 system, we expect it to provide an important testbed for theories of the emplacement and evolution of short-period companions, and theories of tidal dissipation and irradiated brown dwarf atmospheres.
    The Astrophysical Journal 06/2012; 761(2). · 6.73 Impact Factor
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    ABSTRACT: We report the discovery of KELT-2Ab, a hot Jupiter transiting the bright (V=8.77) primary star of the HD 42176 binary system. The host is a slightly evolved late F-star likely in the very short-lived "blue-hook" stage of evolution, with $\teff=6148\pm48{\rm K}$, $\log{g}=4.030_{-0.026}^{+0.015}$ and $\feh=0.034\pm0.78$. The inferred stellar mass is $M_*=1.314_{-0.060}^{+0.063}$\msun\ and the star has a relatively large radius of $R_*=1.836_{-0.046}^{+0.066}$\rsun. The planet is a typical hot Jupiter with period $4.11379\pm0.00001$ days and a mass of $M_P=1.524\pm0.088$\mj\ and radius of $R_P=1.290_{-0.050}^{+0.064}$\rj. This is mildly inflated as compared to models of irradiated giant planets at the $\sim$4 Gyr age of the system. KELT-2A is the third brightest star with a transiting planet identified by ground-based transit surveys, and the ninth brightest star overall with a transiting planet. KELT-2Ab's mass and radius are unique among the subset of planets with $V<9$ host stars, and therefore increases the diversity of bright benchmark systems. We also measure the relative motion of KELT-2A and -2B over a baseline of 38 years, robustly demonstrating for the first time that the stars are bound. This allows us to infer that KELT-2B is an early K-dwarf. We hypothesize that through the eccentric Kozai mechanism KELT-2B may have emplaced KELT-2Ab in its current orbit. This scenario is potentially testable with Rossiter-McLaughlin measurements, which should have an amplitude of $\sim$44 m s$^{-1}$.
    The Astrophysical Journal Letters 06/2012; 756(2). · 6.35 Impact Factor
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    ABSTRACT: I will present the first planetary detections from the KELT-North transit survey. KELT-North is a 42mm robotic camera system at Winer Observatory in Arizona, and survey operations are based out of the Ohio State and Vanderbilt Universities. The KELT-North survey fields are 26 by 26 degrees, and are arranged in a contiguous strip around the sky centered at a declination of +30 degrees. The small aperture and wide field of view of the telescope enables KELT-North to effectively survey some of the brightest stars in the Northern sky for transiting planets. Our focus is on planet candidates around stars between 8 < V < 10. These bright systems are of prime scientific interest, since they provide the best follow-up opportunities from the ground and space. We have been collecting science data since 2006, and actively vetting planet candidates since the spring of 2011. Over the past winter we recorded our first detections of sub-stellar companions. I will briefly discuss KELT-North survey operations before describing the results from our observations of these intriguing systems. We are grateful to the observers and the support staff at the FLWO 60- and 48-inch telescopes. This work was supported by NSF CAREER grant AST-1056524.
    05/2012;
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    ABSTRACT: GM Cep in the young (~4 Myr) open cluster Trumpler 37 has been known to be an abrupt variable and to have a circumstellar disk with very active accretion. Our monitoring observations in 2009-2011 revealed the star to show sporadic flare events, each with brightening of < 0.5 mag lasting for days. These brightening events, associated with a color change toward the blue, should originate from an increased accretion activity. Moreover, the star also underwent a brightness drop of ~1 mag lasting for about a month, during which the star became bluer when fainter. Such brightness drops seem to have a recurrence time scale of a year, as evidenced in our data and the photometric behavior of GM Cep over a century. Between consecutive drops, the star brightened gradually by about 1 mag and became blue at peak luminosity. We propose that the drop is caused by obscuration of the central star by an orbiting dust concentration. The UX Orionis type of activity in GM Cep therefore exemplifies the disk inhomogeneity process in transition between grain coagulation and planetesimal formation in a young circumstellar disk.
    The Astrophysical Journal 03/2012; · 6.73 Impact Factor
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    ABSTRACT: The discovery of transiting planets around bright stars holds the potential to greatly enhance our understanding of planetary atmospheres. The Transit Ephemeris Refinement and Monitoring Survey (TERMS) project focuses on updating the ephemerides of known exoplanets, put tighter constraints on the orbital parameters and shrink the large errors on the predicted transit windows, enabling photometric monitoring to search for a transit signature. Here, we present the revised orbital parameters and the photometric coverage during a predicted transit window of HD168443b, a massive planet orbiting the bright star HD 168443 (V = 6.92) with a period of 58.11 days. The high eccentricity of the planetary orbit (e = 0.53) significantly enhances the a-priori transit probability (3.7%) from what is expected for a circular orbit (2.5%). The transit ephemeris was updated using refined orbital parameters from additional Keck-HIRES radial velocities. The photometry obtained at the 1 m telescope in Cerro Tololo Inter-American Observatory (CTIO) and the T8 0.8 m Automated Photometric Telescope (APT) at Fairborn Observatory achieved the necessary millimag precision. The expected change in flux (0.5%) for HD168443 was not observed during the predicted transit window, thus allowing us to rule out the transit and put tighter constrains on the orbital inclination of HD168443b. Additionally, we present the software used to analyze the CTIO data. Developed by the TERMS team, this IDL based package is a fast, precise, and easy to use program which has eliminated the need for external software and command line prompts by utilizing the functionality of a graphical user interface (GUI).
    01/2012;

Publication Stats

616 Citations
195.74 Total Impact Points

Institutions

  • 1999–2014
    • Swarthmore College
      • Department of Physics and Astronomy
      Swarthmore, Pennsylvania, United States
  • 2013
    • Yale University
      • Department of Astronomy
      New Haven, Connecticut, United States
  • 2008
    • California Institute of Technology
      Pasadena, California, United States
  • 1993–2004
    • University of Wisconsin, Madison
      • Department of Astronomy
      Mississippi, United States
  • 1998
    • Arizona State University
      Phoenix, Arizona, United States