Spitzer photometry and spectroscopy of the star HD 69830 reveal an excess of emission relative to the stellar photosphere between 8 and 35 mu m dominated by strong features attributable to ...crystalline silicates with an emitting surface area more than 1000 times that of our zodiacal cloud. The spectrum closely resembles that of the comet C/1995 O1 (Hale-Bopp). Since no excess is detected at 70 mu m, the emitting material must be quite warm, be confined within a few AU of the star, and originate in grains with low, long-wavelength emissivity, i.e., grains much smaller than 70 mu m/2 pi similar to 10 mu m. The strong mineralogical features are evidence for even smaller, possibly submicron-sized grains. This small grain size is in direct contrast to the 10-100 mu m grains that dominate the relatively featureless spectra of our zodiacal dust cloud and most other main-sequence stars with excesses. The upper limit at 70 mu m also implies that any Kuiper Belt analog must be either very cold or less massive than similar to 5 times our own Kuiper Belt. With collisional and Poynting-Robertson drag times of less than 1000 yr for small grains, the emitting material must either (1) be created through continual grinding down of material in a dense asteroid belt, or (2) originate in cometary debris arising from either a single "supercomet" or a very large number of individual comets arriving from a distant reservoir. In the case of a cometary origin for the emission, the mass requirements for continuous generation by many individual comets are unreasonable, and we favor the capture of a single super comet into a 0.5-1 AU orbit, where it can evolve a large number of small grains over a 2 Myr period.
The Two Micron All Sky Survey (2MASS) Skrutskie, M. F; Cutri, R. M; Stiening, R ...
The Astronomical journal,
02/2006, Volume:
131, Issue:
2
Journal Article
Peer reviewed
Open access
Between 1997 June and 2001 February the Two Micron All Sky Survey (2MASS) collected 25.4 Tbytes of raw imaging data covering 99.998% of the celestial sphere in the near-infrared J (1.25 mm), H (1.65 ...mm), and Ks (2.16 mm) bandpasses. Observations were conducted from two dedicated 1.3 m diameter telescopes located at Mount Hopkins, Arizona, and Cerro Tololo, Chile. The 7.8 s of integration time accumulated for each point on the sky and strict quality control yielded a 10 s point-source detection level of better than 15.8, 15.1, and 14.3 mag at the J, H, and Ks bands, respectively, for virtually the entire sky. Bright source extractions have 1 s photometric uncertainty of <0.03 mag and astrometric accuracy of order 100 mas. Calibration offsets between any two points in the sky are <0.02 mag. The 2MASS All-Sky Data Release includes 4.1 million compressed FITS images covering the entire sky, 471 million source extractions in a Point Source Catalog, and 1.6 million objects identified as extended in an Extended Source Catalog.
We report the discovery of a microlensing planet-MOA-2016-BLG-227Lb-with a large planet/host mass ratio of q 9 × 10−3. This event was located near the K2 Campaign 9 field that was observed by a large ...number of telescopes. As a result, the event was in the microlensing survey area of a number of these telescopes, and this enabled good coverage of the planetary light-curve signal. High angular resolution adaptive optics images from the Keck telescope reveal excess flux at the position of the source above the flux of the source star, as indicated by the light-curve model. This excess flux could be due to the lens star, but it could also be due to a companion to the source or lens star, or even an unrelated star. We consider all these possibilities in a Bayesian analysis in the context of a standard Galactic model. Our analysis indicates that it is unlikely that a large fraction of the excess flux comes from the lens, unless solar-type stars are much more likely to host planets of this mass ratio than lower mass stars. We recommend that a method similar to the one developed in this paper be used for other events with high angular resolution follow-up observations when the follow-up observations are insufficient to measure the lens-source relative proper motion.
Know your audience As with any seminar or presentation, when preparing your job talk, you want to target your specific audience. ...you need to consider the background knowledge and interests of the ...audience members. ...the job talk is a direct measure of your ability to sell your work and to act as an ambassador for the department in your future speaking engagements. ...Rule 4 from 5 is “Make the take-home message persistent,” and this is a particular priority in the swirl of an academic search in which four or five candidates may visit over the span of a few weeks. ...you should also make sure you understand the audiovisual equipment setup in the room where you are giving your presentation.
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ABSTRACT In this paper, we present an analysis of the binary gravitational microlensing event OGLE-2015-BLG-0196. The event lasted for almost a year, and the light curve exhibited significant ...deviations from the lensing model based on the rectilinear lens-source relative motion, enabling us to measure the microlens parallax. The ground-based microlens parallax is confirmed by the data obtained from space-based microlens observations using the Spitzer telescope. By additionally measuring the angular Einstein radius from the analysis of the resolved caustic crossing, the physical parameters of the lens are determined up to the twofold degeneracy, u0 < 0 and u0 > 0, solutions caused by the well-known "ecliptic" degeneracy. It is found that the binary lens is composed of two M dwarf stars with similar masses, M1 = 0.38 0.04 M (0.50 0.05 M ) and M2 = 0.38 0.04 M (0.55 0.06 M ), and the distance to the lens is DL = 2.77 0.23 kpc (3.30 0.29 kpc). Here the physical parameters outside and inside the parentheses are for the u0 < 0 and u0 > 0 solutions, respectively.
Given that low-mass stars have intrinsically low luminosities at optical wavelengths and a propensity for stellar activity, it is advantageous for radial velocity (RV) surveys of these objects to use ...near-infrared (NIR) wavelengths. In this work, we describe and test a novel RV extraction pipeline dedicated to retrieving RVs from low-mass stars using NIR spectra taken by the CSHELL spectrograph at the NASA Infrared Telescope Facility, where a methane isotopologue gas cell is used for wavelength calibration. The pipeline minimizes the residuals between the observations and a spectral model composed of templates for the target star, the gas cell, and atmospheric telluric absorption; models of the line-spread function, continuum curvature, and sinusoidal fringing; and a parameterization of the wavelength solution. The stellar template is derived iteratively from the science observations themselves without a need for separate observations dedicated to retrieving it. Despite limitations from CSHELL's narrow wavelength range and instrumental systematics, we are able to (1) obtain an RV precision of 35 m s−1 for the RV standard star GJ 15 A over a time baseline of 817 days, reaching the photon noise limit for our attained signal-to-noise ratio; (2) achieve ∼3 m s−1 RV precision for the M giant SV Peg over a baseline of several days and confirm its long-term RV trend due to stellar pulsations, as well as obtain nightly noise floors of ∼2-6 m s−1; and (3) show that our data are consistent with the known masses, periods, and orbital eccentricities of the two most massive planets orbiting GJ 876. Future applications of our pipeline to RV surveys using the next generation of NIR spectrographs, such as iSHELL, will enable the potential detection of super-Earths and mini-Neptunes in the habitable zones of M dwarfs.
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Fewer than 20 transiting Kepler planets have periods longer than one year. Our early search of the Kepler light curves revealed one such system, Kepler-1654b (originally KIC 8410697b), which shows ...exactly two transit events and whose second transit occurred only five days before the failure of the second of two reaction wheels brought the primary Kepler mission to an end. A number of authors have also examined light curves from the Kepler mission searching for long-period planets and identified this candidate. Starting in 2014 September, we began an observational program of imaging, reconnaissance spectroscopy, and precision radial velocity (RV) measurements that confirm with a high degree of confidence that Kepler-1654b is a bona fide transiting planet orbiting a mature G5V star (Teff = 5580 K, Fe/H = −0.08) with a semimajor axis of 2.03 au, a period of 1047.84 days, and a radius of 0.82 0.02 RJup. RV measurements using Keck's HIRES spectrometer obtained over 2.5 years set a limit to the planet's mass of <0.5 (3 ) MJup. The bulk density of the planet is similar to that of Saturn or possibly lower. We assess the suitability of temperate gas giants like Kepler-1654b for transit spectroscopy with the James Webb Space Telescope, as their relatively cold equilibrium temperatures (Tpl ∼ 200 K) make them interesting from the standpoint of exoplanet atmospheric physics. Unfortunately, these low temperatures also make the atmospheric scale heights small and thus transmission spectroscopy challenging. Finally, the long time between transits can make scheduling JWST observations difficult-as is the case with Kepler-1654b.
The nearby Sun-like star GJ 758 hosts a cold substellar companion, GJ 758 B, at a projected separation of 30 au, previously detected in high-contrast multi-band photometric observations. In order to ...better constrain the companion's physical characteristics, we acquired the first low-resolution (R ∼ 50) near-infrared spectrum of it using the high-contrast hyperspectral imaging instrument Project 1640 on Palomar Observatory's 5 m Hale telescope. We obtained simultaneous images in 32 wavelength channels covering the Y, J, and H bands (∼952-1770 nm), and used data processing techniques based on principal component analysis to efficiently subtract chromatic background speckle-noise. GJ 758 B was detected in four epochs during 2013 and 2014. Basic astrometric measurements confirm its apparent northwest trajectory relative to the primary star, with no clear signs of orbital curvature. Spectra of SpeX/IRTF observed T dwarfs were compared to the combined spectrum of GJ 758 B, with χ2 minimization suggesting a best fit for spectral type T7.0 1.0, but with a shallow minimum over T5-T8. Fitting of synthetic spectra from the BT-Settl13 model atmospheres gives an effective temperature Teff = 741 25 K and surface gravity dex (cgs). Our derived best-fit spectral type and effective temperature from modeling of the low-resolution spectrum suggest a slightly earlier and hotter companion than previous findings from photometric data, but do not rule out current results, and confirm GJ 758 B as one of the coolest sub-stellar companions to a Sun-like star to date.
ABSTRACT We report the first mass and distance measurements of a caustic-crossing binary system OGLE-2014-BLG-1050 L using the space-based microlens parallax method. Spitzer captured the second ...caustic crossing of the event, which occurred ∼10 days before that seen from Earth. Due to the coincidence that the source-lens relative motion was almost parallel to the direction of the binary-lens axis, the fourfold degeneracy, which was known before only to occur in single-lens events, persists in this case, leading to either a lower-mass (0.2 and 0.07 ) binary at ∼1.1 kpc or a higher-mass (0.9 and 0.35 ) binary at ∼3.5 kpc. However, the latter solution is strongly preferred for reasons including blending and lensing probability. OGLE-2014-BLG-1050 L demonstrates the power of microlens parallax in probing stellar and substellar binaries.
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