| 1. |
- de Wijn, A. G., et al.
(author)
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Design and Performance Analysis of a Highly Efficient Polychromatic Full Stokes Polarization Modulator for the CRISP Imaging Spectrometer
- 2021
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 161:2
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Journal article (peer-reviewed)abstract
- We present the design and performance of a polychromatic polarization modulator for the CRisp Imaging SpectroPolarimeter (CRISP) Fabry-Perot tunable narrow-band imaging spectropolarimer at the Swedish 1 m Solar Telescope (SST). We discuss the design process in depth, compare two possible modulator designs through a tolerance analysis, and investigate thermal sensitivity of the selected design. The trade-offs and procedures described in this paper are generally applicable in the development of broadband polarization modulators. The modulator was built and has been operational since 2015. Its measured performance is close to optimal between 500 and 900 nm, and differences between the design and as-built modulator are largely understood. We show some example data, and briefly review scientific work that used data from SST/CRISP and this modulator.
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| 2. |
- Uyama, Taichi, et al.
(author)
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Atmospheric Characterization and Further Orbital Modeling of kappa Andromeda b
- 2020
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 159:2
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Journal article (peer-reviewed)abstract
- We present kappa Andromeda b's photometry and astrometry taken with Subaru/SCExAO+HiCIAO and Keck/NIRC2, combined with recently published SCExAO/CHARIS low-resolution spectroscopy and published thermal infrared photometry to further constrain the companion's atmospheric properties and orbit. The Y/Y-K colors of kappa And b are redder than field dwarfs, consistent with its youth and lower gravity. Empirical comparisons of its Y-band photometry and CHARIS spectrum to a large spectral library of isolated field dwarfs reaffirm the conclusion from Currie et al. that it likely has a low gravity but admit a wider range of most plausible spectral types (L0-L2). Our gravitational classification also suggests that the best-fit objects for kappa And b may have lower gravity than those previously reported. Atmospheric models lacking dust/clouds fail to reproduce its entire 1-4.7 mu m spectral energy distribution (SED), and cloudy atmosphere models with temperatures of similar to 1700-2000 K better match kappa And b data. Most well-fitting model comparisons favor 1700-1900 K, a surface gravity of log(g) similar to 4-4.5, and a radius of 1.3-1.6 R-Jup; the best-fit model (Drift-Phoenix) yields the coolest and lowest-gravity values: T-eff = 1700 K and log g = 4.0. An update to kappa And b's orbit with ExoSOFT using new astrometry spanning 7 yr reaffirms its high eccentricity (0.77 0.08). We consider a scenario where unseen companions are responsible for scattering kappa And b to a wide separation and high eccentricity. If three planets, including kappa And b, were born with coplanar orbits, and one of them was ejected by gravitational scattering, a potential inner companion with mass greater than or similar to 10 M-Jup could be located at less than or similar to 25 au.
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| 3. |
- Viswanath, Gayathri, 1992-, et al.
(author)
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A Statistical Search for Star–Planet Interaction in the Ultraviolet Using GALEX
- 2020
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 159:5, s. 194-194
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Journal article (peer-reviewed)abstract
- Most (∼82%) of the over 4000 confirmed exoplanets known today orbit very close to their host stars, within 0.5 au. Planets at such small orbital distances can result in significant interactions with their host stars, which can induce increased activity levels in them. In this work, we have searched for statistical evidence for star–planet interactions in the ultraviolet (UV) using the largest sample of 1355 Galaxy Evolution Explorer (GALEX) detected host stars with confirmed exoplanets and making use of the improved host-star parameters from Gaia DR2. From our analysis, we do not find any significant correlation between the UV activity of the host stars and their planetary properties. We further compared the UV properties of planet host stars to that of chromospherically active stars from the RAdial Velocity Experiment (RAVE) survey. Our results indicate that the enhancement in chromospheric activity of host stars due to star–planet interactions may not be significant enough to reflect in their near- and far-UV broadband flux.
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| 4. |
- Youngblood, Allison, et al.
(author)
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A Radiatively Driven Wind from the η Tel Debris Disk
- 2021
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 162:6
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Journal article (peer-reviewed)abstract
- We present far- and near-ultraviolet absorption spectroscopy of the ∼23 Myr edge-on debris disk surrounding the A0V star η Telescopii, obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph. We detect absorption lines from C i, C ii, O i, Mg ii, Al ii, Si ii, S ii, Mn ii, Fe ii, and marginally N i. The lines show two clear absorption components at −22.7 ± 0.5 km s−1 and −17.8 ± 0.7 km s−1, which we attribute to circumstellar (CS) and interstellar gas, respectively. CO absorption is not detected, and we find no evidence for star-grazing exocomets. The CS absorption components are blueshifted by −16.9 ± 2.6 km s−1 in the star's reference frame, indicating that they are outflowing in a radiatively driven disk wind. We find that the C/Fe ratio in the η Tel CS gas is significantly higher than the solar ratio, as is the case in the β Pic and 49 Cet debris disks. Unlike those disks, however, the measured C/O ratio in the η Tel CS gas is consistent with the solar value. Our analysis shows that because η Tel is an earlier type star than β Pic and 49 Cet, with more substantial radiation pressure at the dominant C ii transitions, this species cannot bind the CS gas disk to the star as it does for β Pic and 49 Cet, resulting in the disk wind.
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| 5. |
- Foley, Ryan J., et al.
(author)
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ON THE PROGENITOR AND SUPERNOVA OF THE SN 2002cx-LIKE SUPERNOVA 2008ge
- 2010
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 140:5, s. 1321-1328
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Journal article (peer-reviewed)abstract
- We present observations of supernova (SN) 2008ge, which is spectroscopically similar to the peculiar SN 2002cx, and its pre-explosion site indicating that its progenitor was probably a white dwarf. NGC 1527, the host galaxy of SN 2008ge, is an S0 galaxy with no evidence of star formation or massive stars. Astrometrically matching late-time imaging of SN 2008ge to pre-explosion Hubble Space Telescope imaging, we constrain the luminosity of the progenitor star. Since SN 2008ge has no indication of hydrogen or helium in its spectrum, its progenitor must have lost its outer layers before exploding, meaning that it is a white dwarf, a Wolf-Rayet star, or a lower-mass star in a binary system. Observations of the host galaxy show no signs of individual massive stars, star clusters, or H (II) regions at the SN position or anywhere else, making a Wolf-Rayet progenitor unlikely. Late-time spectroscopy of SN 2008ge shows strong [Fe (II)] lines with large velocity widths compared to other members of this class at similar epochs. These previously unseen features indicate that a significant amount of the SN ejecta is Fe (presumably the result of the radioactive decay of Ni-56 generated in the SN), further supporting a thermonuclear explosion. Placing the observations of SN 2008ge in the context of observations of other objects in the same class of SNe, we suggest that the progenitor was most likely a white dwarf.
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| 6. |
- Roberts, Lewis C., et al.
(author)
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CHARACTERIZATION OF THE COMPANION mu HER
- 2016
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 151:6
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Journal article (peer-reviewed)abstract
- mu Her is a nearby quadruple system with a G-subgiant primary and several low-mass companions arranged in a 2+2 architecture. While the BC components have been well characterized, the Ab component has been detected astrometrically and with direct imaging but there has been some confusion over its nature, in particular, whether the companion is stellar or substellar. Using near-infrared spectroscopy, we are able to estimate the spectral type of the companion as an M4 +/- 1V star. In addition, we have measured the astrometry of the system for over a decade. We combined the astrometry with archival radial velocity measurements to compute an orbit of the system. From the combined orbit, we are able to compute the mass sum of the system. Using the estimated mass of the primary, we estimate the mass of the secondary as 0.32 MG, which agrees with the estimated spectral type. Our computed orbit is preliminary due to the incomplete orbital phase coverage, but it should be sufficient to predict ephemerides over the next decade.
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| 7. |
- Agarwal, Sahil, et al.
(author)
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Minimal Data Fidelity for Stellar Feature and Companion Detection
- 2022
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 163:1, s. 6-
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Journal article (peer-reviewed)abstract
- Technological advances in instrumentation have led to an exponential increase in exoplanet detection and scrutiny of stellar features such as spots and faculae. While the spots and faculae enable us to understand the stellar dynamics, exoplanets provide us with a glimpse into stellar evolution. While the ubiquity of noise (e.g., telluric, instrumental, or photonic) is unavoidable, combining this with increased spectrographic resolution compounds technological challenges. To account for these noise sources and resolution issues, we use a temporal multifractal framework to study data from the Spot Oscillation And Planet 2.0 tool, which simulates a stellar spectrum in the presence of a spot, a facula or a planet. Given these controlled simulations, we vary the resolution as well as the signal-to-noise ratio (S/N) to obtain a lower limit on the resolution and S/N required to robustly detect features. We show that a spot and a facula with a 1% coverage of the stellar disk can be robustly detected for a S/N (per pixel) of 35 and 60, respectively, for any spectral resolution above 20,000, while a planet with a radial velocity of 10 m s(-1) can be detected for a S/N (per pixel) of 600. Rather than viewing noise as an impediment, our approach uses noise as a source of information.
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| 8. |
- Alsubai, Khalid, et al.
(author)
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Qatar Exoplanet Survey : Qatar-3b, Qatar-4b, and Qatar-5b
- 2017
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 153:4
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Journal article (peer-reviewed)abstract
- We report the discovery of Qatar-3b, Qatar-4b, and Qatar-5b, three new transiting planets identified by the Qatar Exoplanet Survey. The three planets belong to the hot Jupiter family, with orbital periods of P-Q3b = 2.50792 days, P-Q4b = 1.80539 days, and P-Q5b = 2.87923 days. Follow-up spectroscopic observations reveal the masses of the planets to be M-Q3b = 4.31 +/- 0.47 M-J, M-Q4b = 6.10 +/- 0.54 M-J, and M-Q5b = 4.32 +/- 0.18 M-J, while model fits to the transit light curves yield radii of R-Q3b = 1.096 +/- 0.14 RJ, R-Q4b = 1.135 +/- 0.11 R-J, and R-Q5b = 1.107 +/- 0.064 R-J. The host stars are low-mass main sequence stars with masses and radii M-Q3 = 1.145 +/- 0.064 M circle dot, M-Q4 = 0.896 +/- 0.048 M circle dot, M-Q5 = 1.128 +/- 0.056 M circle dot and R-Q3 = 1.272 +/- 0.14 R circle dot, R-Q4 = 0.849 +/- 0.063 R circle dot, and R-Q5 = 1.076 +/- 0.051 R circle dot for Qatar-3, 4, and 5 respectively. The V magnitudes of the three host stars are V-Q3 = 12.88, V-Q4 = 13.60, and V-Q5 = 12.82. All three new planets can be classified as heavy hot Jupiters (M > 4 M-J).
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| 9. |
- Baron, Frédérique, et al.
(author)
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WEIRD : Wide-orbit Exoplanet Search with InfraRed Direct Imaging
- 2018
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 156:3
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Journal article (peer-reviewed)abstract
- We report results from the Wide-orbit Exoplanet search with InfraRed Direct imaging, or WEIRD, a survey designed to search for Jupiter-like companions on very wide orbits (1000-5000 au) around young stars (<120 Myr) that are known members of moving groups in the solar neighborhood (<70 pc). Companions that share the same age, distance, and metallicity as their host while being on large enough orbits to be studied as isolated objects make prime targets for spectroscopic observations, and they are valuable benchmark objects for exoplanet atmosphere models. The search strategy is based on deep imaging in multiple bands across the near-infrared domain For all 177 objects of our sample, z(ab)', J, [3.6], and [4.5] images were obtained with CFHT/MegaCam, GEMINI/GMOS, CFHT/WIRCam, GEMINI/Flamingos-2, and Spitzer IIRAC. Using this set of four images per target, we searched for sources with red z(ab)' and [3.6]-[4.5] colors, typically reaching good completeness down to 2 M-J(up) companions, while going down to 1 M-J(up) for some targets, at separations of 1000-5000 au. The search yielded four candidate companions with the expected colors, but they were all rejected through follow-up proper motion observations. Our results constrain the occurrence of 1-13 M(J)(u)p planetary-mass companions on orbits with a semimajor axis between 1000 and 5000 au at less than 0.03, with a 95% confidence level.
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| 10. |
- Bolin, Bryce T., et al.
(author)
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Characterization of the Nucleus, Morphology, and Activity of Interstellar Comet 2I/Borisov by Optical and Near-infrared GROWTH, Apache Point, IRTF, ZTF, and Keck Observations
- 2020
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 160:1
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Journal article (peer-reviewed)abstract
- We present visible and near-infrared (NIR) photometric and spectroscopic observations of interstellar object (ISO) 2I/Borisov taken from 2019 September 10 to 2019 December 20 using the GROWTH, the Apache Point Observatory Astrophysical Research Consortium 3.5 m, and the NASA Infrared Telescope Facility 3.0 m combined with pre- and postdiscovery observations of 2I obtained by the Zwicky Transient Facility from 2019 March 17 to 2019 May 5. Comparison with imaging of distant solar system comets shows an object very similar to mildly active solar system comets with an outgassing rate of similar to 10(27)mol s(-1). The photometry, taken in filters spanning the visible and NIR range, shows a gradual brightening trend of similar to 0.03 mag day(-1)since 2019 September 10 UTC for a reddish object becoming neutral in the NIR. The light curve from recent and prediscovery data reveals a brightness trend suggesting the recent onset of significant H2O sublimation with the comet being active with super volatiles such as CO at heliocentric distances >6 au consistent with its extended morphology. Using the advanced capability to significantly reduce the scattered light from the coma enabled by high-resolution NIR images from Keck adaptive optics taken on 2019 October 4, we estimate a diameter for 2I's nucleus of less than or similar to 1.4 km. We use the size estimates of 1I/'Oumuamua and 2I/Borisov to roughly estimate the slope of the ISO size distribution, resulting in a slope of similar to 3.4 1.2, similar to solar system comets and bodies produced from collisional equilibrium.
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