scholarly journals Gemini/GMOS Transmission Spectroscopy of the Grazing Planet Candidate WD 1856+534 b

2021 ◽  
Vol 162 (6) ◽  
pp. 296
Author(s):  
Siyi Xu ◽  
Hannah Diamond-Lowe ◽  
Ryan J. MacDonald ◽  
Andrew Vanderburg ◽  
Simon Blouin ◽  
...  
Keyword(s):  
Transmission Spectrum ◽  
Main Sequence ◽  
Giant Planet ◽  
Stellar Disk ◽  
Atmospheric Models ◽  
Content Type ◽  
Substellar Objects ◽  
Type Object ◽  
Limb Darkening ◽  
Absorption Features

Abstract WD 1856+534 b is a Jupiter-sized, cool giant planet candidate transiting the white dwarf WD 1856+534. Here, we report an optical transmission spectrum of WD 1856+534 b obtained from ten transits using the Gemini Multi-Object Spectrograph. This system is challenging to observe due to the faintness of the host star and the short transit duration. Nevertheless, our phase-folded white light curve reached a precision of 0.12%. WD 1856+534 b provides a unique transit configuration compared to other known exoplanets: the planet is 8× larger than its star and occults over half of the stellar disk during mid-transit. Consequently, many standard modeling assumptions do not hold. We introduce the concept of a “limb darkening corrected, time-averaged transmission spectrum” and propose that this is more suitable than ( R p , λ / R s ) 2 for comparisons to atmospheric models for planets with grazing transits. We also present a modified radiative transfer prescription. Though the transmission spectrum shows no prominent absorption features, it is sufficiently precise to constrain the mass of WD 1856+534 b to be >0.84 M J (to 2σ confidence), assuming a clear atmosphere and a Jovian composition. High-altitude cloud decks can allow lower masses. WD 1856+534 b could have formed either as a result of common envelope evolution or migration under the Kozai–Lidov mechanism. Further studies of WD 1856+534 b, alongside new dedicated searches for substellar objects around white dwarfs, will shed further light on the mysteries of post-main-sequence planetary systems.

scholarly journals Correcting the effect of stellar spots on ARIEL transmission spectra II. The limb darkening effect

2021 ◽  
Author(s):  
G Cracchiolo ◽  
G Micela ◽  
G Morello ◽  
G Peres
Keyword(s):  
Impact Parameter ◽  
Transmission Spectrum ◽  
Stellar Disk ◽  
Transmission Spectra ◽  
Potential Bias ◽  
Temperature Contrast ◽  
Planetary Transmission ◽  
Limb Darkening ◽  
The Impact

Abstract This paper is part of an effort to correct the transmission spectra of a transiting planet orbiting an active star. In Paper I (Cracchiolo et al. 2020) we have demonstrated a methodology to minimize the potential bias induced by unocculted star spots on the transmission spectrum, assuming a spot model parameterized by filling factor and temperature. In this work we introduce the limb darkening effect, therefore the position of the spot in the stellar disk and the impact parameter of the transiting planet now play a key role. The method is tested on simulations of planetary transits of three representative kinds of planetary systems, at ARIEL resolution. We find that a realistic treatment of the limb darkening is required to reliably estimate both the spots parameters and the transmission spectrum of the transiting planet. Furthermore, we show that the influence of the spots on the retrieval of the planetary transmission spectrum is significant for spots close to the center of the star, covering a fraction greater than 0.05 and with a temperature contrast greater than 500 K, and that for these cases our method can confidently extract the transmission spectrum and the impact parameter of the transiting planet for both cases of occulted and not occulted spots, provided that we have an accurate characterization of the stellar parameters and a reliable simulator of the instrument performances.

scholarly journals The highly inflated giant planet WASP-174b

2020 ◽  
Vol 633 ◽  
pp. A30 ◽  
Author(s):  
L. Mancini ◽  
P. Sarkis ◽  
Th. Henning ◽  
G. Á. Bakos ◽  
D. Bayliss ◽  
...  
Keyword(s):  
Main Sequence ◽  
Giant Planet ◽  
Empirical Method ◽  
Photometric Data ◽  
Physical Parameters ◽  
Good Target ◽  
Limb Darkening ◽  
Measured Mass ◽  
Parent Star

Context. The transiting exoplanetary system WASP-174 was reported to be composed by a main-sequence F star (V = 11.8 mag) and a giant planet, WASP-174b (orbital period Porb = 4.23 days). However only an upper limit was placed on the planet mass (<1.3 MJup), and a highly uncertain planetary radius (0.7−1.7 RJup) was determined. Aims. We aim to better characterise both the star and the planet and precisely measure their orbital and physical parameters. Methods. In order to constrain the mass of the planet, we obtained new measurements of the radial velocity of the star and joined them with those from the discovery paper. Photometric data from the HATSouth survey and new multi-band, high-quality (precision reached up to 0.37 mmag) photometric follow-up observations of transit events were acquired and analysed for getting accurate photometric parameters. We fit the model to all the observations, including data from the TESS space telescope, in two different modes: incorporating the stellar isochrones into the fit, and using an empirical method to get the stellar parameters. The two modes resulted to be consistent with each other to within 2σ. Results. We confirm the grazing nature of the WASP-174b transits with a confidence level greater than 5σ, which is also corroborated by simultaneously observing the transit through four optical bands and noting how the transit depth changes due to the limb-darkening effect. We estimate that ≈76% of the disk of the planet actually eclipses the parent star at mid-transit of its transit events. We find that WASP-174b is a highly-inflated hot giant planet with a mass of Mp = 0.330 ± 0.091 MJup and a radius of Rp = 1.435 ± 0.050 RJup, and is therefore a good target for transmission-spectroscopy observations. With a density of ρp = 0.135 ± 0.042 g cm−3, it is amongst the lowest-density planets ever discovered with precisely measured mass and radius.

scholarly journals Deeply Buried Nuclei in the Infrared-luminous Galaxies NGC 4418 and Arp 220. II. Line Forests at λ = 1.4–0.4 mm and Circumnuclear Gas Observed with ALMA

2021 ◽  
Vol 923 (2) ◽  
pp. 240
Author(s):  
Kazushi Sakamoto ◽  
Sergio Martín ◽  
David J. Wilner ◽  
Susanne Aalto ◽  
Aaron S. Evans ◽  
...  
Keyword(s):  
Galactic Disk ◽  
Vibrationally Excited ◽  
Content Type ◽  
Counter Rotation ◽  
Luminous Galaxies ◽  
Line Absorption ◽  
Type Object ◽  
Upper Level ◽  
Array Imaging ◽  
The Continuum

Abstract We present the line observations in our Atacama Millimeter-Submillimeter Array imaging spectral scan toward three deeply buried nuclei in NGC 4418 and Arp 220. We cover 67 GHz in f rest = 215–697 GHz at about 0.″2 (30, 80 pc) resolution. All the nuclei show dense line forests; we report our initial line identification using 55 species. The line velocities generally indicate gas rotation around each nucleus, tracing nuclear disks of ∼100 pc in size. We confirmed the counter-rotation of the nuclear disks in Arp 220 and that of the nuclear disk and the galactic disk in NGC 4418. While the brightest lines exceed 100 K, most of the major lines and many 13C isotopologues show absorption against even brighter continuum cores of the nuclei. The lines with higher upper-level energies, including those from vibrationally excited molecules, tend to arise from smaller areas, indicating radially varying conditions in these nuclei. The outflows from the two Arp 220 nuclei cause blueshifted line absorption below the continuum level. The absorption mostly has small spatial offsets from the continuum peaks to indicate the outflow orientations. The bipolar outflow from the western nucleus is also imaged in multiple emission lines, showing the extent of ∼1″ (400 pc). Redshifted line absorption against the nucleus of NGC 4418 indicates either an inward gas motion or a small collimated outflow slanted to the nuclear disk. We also resolved some previous confusions due to line blending and misidentification.

scholarly journals Activity time series of old stars from late F to early K

2019 ◽  
Vol 629 ◽  
pp. A42 ◽  
Author(s):  
N. Meunier ◽  
A.-M. Lagrange
Keyword(s):  
Time Series ◽  
Main Sequence ◽  
Stellar Disk ◽  
Physical Parameters ◽  
Activity Levels ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Photometric Variability ◽  
Chromospheric Emission ◽  
Brightness Variability

Context. A number of high-precision time series have recently become available for many stars as a result of data from CoRoT, Kepler, and TESS. These data have been widely used to study stellar activity. Photometry provides information that is integrated over the stellar disk. Therefore, there are many degeneracies between spots and plages or sizes and contrasts. In addition, it is important to relate activity indicators, derived from photometric light curves, to other indicators (Log R′HK and radial velocities). Aims. Our aim is to understand how to relate photometric variability to physical parameters in order to help the interpretation of these observations. Methods. We used a large number of synthetic time series of brightness variations for old main sequence stars within the F6-K4 range. Simultaneously, we computed using consistent modeling for radial velocity, astrometry, and chromospheric emission. We analyzed these time series to study the effect of the star spectral type on brightness variability, the relationship between brightness variability and chromospheric emission, and the interpretation of brightness variability as a function of spot and plage properties. We then studied spot-dominated or plage-dominated regimes. Results. We find that within our range of activity levels, the brightness variability increases toward low-mass stars, as suggested by Kepler results. However, many elements can create an interpretation bias. Brightness variability roughly correlates to Log R′HK level. There is, however, a large dispersion in this relationship, mostly caused by spot contrast and inclination. It is also directly related to the number of structures, and we show that it can not be interpreted solely in terms of spot sizes. Finally, a detailed analysis of its relation with Log R′HK shows that in the activity range of old main-sequence stars, we can obtain both spot or plage dominated regimes, as was shown by observations in previous works. The same star can also be observed in both regimes depending on inclination. Furthermore, only strong correlations between chromospheric emission and brightness variability are significant. Conclusions. Our realistic time series proves to be extremely useful when interpreting observations and understanding their limitations, most notably in terms of activity interpretation. Inclination is crucial and affects many properties, such as amplitudes and the respective role of spots and plages.

scholarly journals Dynamical masses for the nearest brown dwarf binary: ε Indi Ba,b

2009 ◽  
Vol 5 (H15) ◽  
pp. 761-761
Author(s):  
C. V. Cardoso ◽  
M. J. McCaughrean ◽  
R. R. King ◽  
L. M. Close ◽  
R.-D. Scholz ◽  
...  
Keyword(s):  
Main Sequence ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Atmospheric Models ◽  
Brown Dwarf ◽  
Near Ir ◽  
The Earth ◽  
Benchmark System ◽  
Model Independent ◽  
Dynamical Masses

Binary brown dwarfs are important because their dynamical masses can be determined in a model-independent way. If a main sequence star is also involved, the age and metallicity for the system can be determined, making it possible to break the sub-stellar mass-age degeneracy. The most suitable benchmark system for intermediate age T dwarfs is ε Indi Ba,b, two T dwarfs (spectral types T1 and T6; McCaughrean et al. (2004)) orbiting a K4.5V star, ε Indi A, at a projected separation of 1460AU. At a distance of 3.6224pc (HIPPARCOS distance to ε Indi A; van Leeuwen (2007)), these are the closest brown dwarfs to the Earth, and thus both components are bright and the system is well-resolved. The system has been monitored astrometrically with NACO and FORS2 on the VLT since June 2004 and August 2005, respectively, in order to determine the system and individual masses independent of evolutionary models. We have obtained a preliminary system mass of 121±1MJup. We have also analysed optical/near-IR spectra (0.6-5.0μm at a resolution up to R~5000; King et al. (2009)) allowing us to determine bolometric luminosities, compare and calibrate evolutionary and atmospheric models of T dwarfs at an age of 4-8Gyr.

scholarly journals What Do Young Brown Dwarfs Tell Us About Exoplanets?

2015 ◽  
Vol 10 (S314) ◽  
pp. 226-231
Author(s):  
Katelyn N. Allers ◽  
Michael C. Liu ◽  
Trent J. Dupuy
Keyword(s):  
Effective Temperature ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Atmospheric Models ◽  
Sky Surveys ◽  
Fundamental Properties ◽  
Dust Clouds ◽  
Planetary Mass ◽  
Substellar Objects ◽  
Successes And Challenges

AbstractIn recent years, all-sky surveys have uncovered a new and interesting population of young (≈10–200 Myr), nearby substellar objects. Many of these objects have inferred masses and temperatures that overlap those of directly imaged exoplanets. These young brown dwarfs provide valuable analogs to young, dusty exoplanets in a context where detailed spectroscopic observations across a broad range of wavelengths and at high S/N are possible. How do the temperatures inferred by atmospheric models and evolutionary models compare? Can we determine the formation mechanism of a young planetary-mass object? How well do we understand the role that disequilibrium chemistry and dust clouds play in the atmospheres of these objects? We review the successes and challenges in determining the fundamental properties (mass, log(g), effective temperature) of young substellar objects, both brown dwarfs and gas-giant exoplanets.

scholarly journals Very Low Mass Stars and Brown Dwarf Candidates in Orion OB1a and OB1b

2003 ◽  
Vol 211 ◽  
pp. 119-122
Author(s):  
Frederick M. Walter ◽  
William H. Sherry ◽  
Scott J. Wolk
Keyword(s):  
Ir Spectroscopy ◽  
Main Sequence ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
Space Density ◽  
Near Ir ◽  
Substellar Objects ◽  
Low Mass ◽  
M Stars

VRI images within the belt of Orion and the Ori OB1a association reveal a pre-main sequence locus extending to below our completeness limit of about V=21. We report here on followup JHK imaging and optical and near–IR spectroscopy of the faintest and reddest of the PMS candidates. We find that they are unreddened mid-to-late M “stars” which fall on a few million year isochrone. Masses are largely substellar, reaching as low as about 0.02 M⊙ (20 Jovian masses). The space density of the substellar objects is high.

scholarly journals Properties which cannot be explained by Planetary Nebulae's progenitors

1997 ◽  
Vol 180 ◽  
pp. 367-367
Author(s):  
Noam Soker
Keyword(s):  
Main Sequence ◽  
Brown Dwarfs ◽  
Giant Planets ◽  
Main Sequence Stars ◽  
Substellar Objects ◽  
Earth Like Planets ◽  
Low Mass ◽  
Inner Region ◽  
Central Stars

Stellar binary companions account for bipolar PNe (∼ 11% of all PNe1), and some ellipticalls (22%2). The rest of axisymmetrical PNe (40% to 60% of all PNe) are due to substellar objects (planets and brown dwarfs)3. This classification of axi symmetrical PNe suggests that substellar objects are commonly present within several × AU around main sequence stars, and that several substellar objects must be present around most main sequence stars3. Some substellar and low mass stellar companions will enter the primary envelope only as the primary reaches the upper AGB. Thus, the early mass loss episode will be spherical, leading to the formation of a spherical halo around an elliptical inner region. Gas giant planets and brown dwarfs close to the primary, will not allow Earth-like planets to have stable orbits. Systems with no Jupiter-like planets will allow Earth-like planets to be present. These stars will form spherical PNe (10%-20% of all PNe, including spherically ejected PNe that have been deformed by the ISM through which they move4). Systems with substellar objects at large separation, as Jupiter in the solar system, will also allow Earth-like planets to be present. These systems will form PNe with spherical halo. Therefore, life may have been present in planets around the central stars of round PNe and elliptical PNe with round halos.

Ammonium abundance and short-wave infrared absorption spectra of altered rocks

2020 ◽  
Vol 20 (4) ◽  
pp. 451-460
Author(s):  
Keiko Hattori ◽  
Anna Fonseca ◽  
Tabetha Sheppard
Keyword(s):  
Absorption Spectra ◽  
Nitrogen Isotope ◽  
Short Wave ◽  
Absorption Feature ◽  
Rock Composition ◽  
Content Type ◽  
Fine Grained ◽  
Supplementary Material ◽  
Short Wave Infrared ◽  
Absorption Features

Rhyolitic rocks hosting the El Zapote epithermal Ag deposit are pervasively altered and contain ammonium ranging from 290 to 1750 ppm. High ammonium values are found in samples containing abundant fine-grained illite. This fine-grained illite shows overall low ratios of K/(Al + Fe), likely due to ammonium substituting K+. Samples containing high ammonium, greater than 1000 ppm in the proximity of Ag-bearing veins, show distinct absorption features of ammonium in short-wave infrared (SWIR) absorption spectra. Samples containing ammonium ranging from 500 to 1000 ppm show mixed absorption signatures; some show prominent absorption features related to ammonium, whereas others have no recognizable features. There is no discernible absorption feature related to ammonium for samples containing less than 500 ppm NH4. The data suggest that SWIR spectroscopy is useful in locating the proximal areas to mineralization, but the extent of ammonium alteration is much larger than that identified by SWIR spectroscopy. Nitrogen isotope compositions of ammonium are similar to those of sedimentary rocks, suggesting that the source of ammonium in altered rhyolite is sedimentary basement rocks in the area.Supplementary material: bulk rock composition is available at https://doi.org/10.6084/m9.figshare.c.5015663

scholarly journals Interferometric Fringe Visibility Null as a Function of Spatial Frequency: A Probe of Stellar Atmospheres

2019 ◽  
Vol 08 (04) ◽  
pp. 1950012
Author(s):  
J. T. Armstrong ◽  
A. M. Jorgensen ◽  
D. Mozurkewich ◽  
H. R. Neilson ◽  
E. K. Baines ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Angular Size ◽  
Brightness Distribution ◽  
Stellar Atmosphere ◽  
Stellar Atmospheres ◽  
Stellar Disk ◽  
Baseline Length ◽  
Fringe Visibility ◽  
Multiple Wavelengths ◽  
Limb Darkening

We introduce an observational tool based on visibility nulls in optical spectro-interferometry fringe data to probe the structure of stellar atmospheres. In a preliminary demonstration, we use both Navy Precision Optical Interferometer (NPOI) data and stellar atmosphere models to show that this tool can be used, for example, to investigate limb darkening. Using bootstrapping with either multiple linked baselines or multiple wavelengths in optical and infrared spectro-interferometric observations of stars makes it possible to measure the spatial frequency [Formula: see text] at which the real part of the fringe visibility [Formula: see text] vanishes. That spatial frequency is determined by [Formula: see text], where [Formula: see text] is the projected baseline length, and [Formula: see text] is the wavelength at which the null is observed. Since [Formula: see text] changes with the Earth’s rotation, [Formula: see text] also changes. If [Formula: see text] is constant with wavelength, [Formula: see text] varies in direct proportion to [Formula: see text]. Any departure from that proportionality indicates that the brightness distribution across the stellar disk varies with wavelength via variations in limb darkening, in the angular size of the disk, or both. In this paper, we introduce the use of variations of [Formula: see text] with [Formula: see text] as a means of probing the structure of stellar atmospheres. Using the equivalent uniform disk diameter [Formula: see text], given by [Formula: see text], as a convenient and intuitive parameterization of [Formula: see text], we demonstrate this concept by using model atmospheres to calculate the brightness distribution for [Formula: see text] Ophiuchi and to predict [Formula: see text], and then comparing the predictions to coherently averaged data from observations taken with the NPOI.

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