scholarly journals Are inner disc misalignments common? ALMA reveals an isotropic outer disc inclination distribution for young dipper stars

2019 ◽  
Vol 492 (1) ◽  
pp. 572-588 ◽  
Author(s):  
M Ansdell ◽  
E Gaidos ◽  
C Hedges ◽  
M Tazzari ◽  
A L Kraus ◽  
...  
Keyword(s):  
Variable Star ◽  
Selection Effect ◽  
Occurrence Rate ◽  
Thick Disc ◽  
Observational Selection ◽  
Isotropic Distribution ◽  
Host Stars ◽  
Protoplanetary Discs

ABSTRACT Dippers are a common class of young variable star exhibiting day-long dimmings with depths of up to several tens of per cent. A standard explanation is that dippers host nearly edge-on (id ≈ 70°) protoplanetary discs that allow close-in (<1 au) dust lifted slightly out of the mid-plane to partially occult the star. The identification of a face-on dipper disc and growing evidence of inner disc misalignments brings this scenario into question. Thus, we uniformly (re)derive the inclinations of 24 dipper discs resolved with (sub-)mm interferometry from ALMA. We find that dipper disc inclinations are consistent with an isotropic distribution over id ≈ 0−75°, above which the occurrence rate declines (likely an observational selection effect due to optically thick disc mid-planes blocking their host stars). These findings indicate that the dipper phenomenon is unrelated to the outer (>10 au) disc resolved by ALMA and that inner disc misalignments may be common during the protoplanetary phase. More than one mechanism may contribute to the dipper phenomenon, including accretion-driven warps and ‘broken’ discs caused by inclined (sub-)stellar or planetary companions.

scholarly journals The dust never settles: collisional production of gas and dust in evolved planetary systems

2020 ◽  
Vol 496 (4) ◽  
pp. 5233-5242 ◽  
Author(s):  
Andrew Swan ◽  
Jay Farihi ◽  
Thomas G Wilson ◽  
Steven G Parsons
Keyword(s):  
Time Scales ◽  
White Dwarf ◽  
Dust Emission ◽  
Canonical Model ◽  
Minor Planets ◽  
Infrared Photometry ◽  
Dust Production ◽  
Thick Disc ◽  
Observed Behaviour ◽  
Host Stars

ABSTRACT Multi-epoch infrared photometry from Spitzer is used to monitor circumstellar discs at white dwarfs, which are consistent with disrupted minor planets whose debris is accreted and chemically reflected by their host stars. Widespread infrared variability is found across the population of 37 stars with two or more epochs. Larger flux changes occur on longer time-scales, reaching several tens of per cent over baselines of a few years. The canonical model of a geometrically thin, optically thick disc is thus insufficient, as it cannot give rise to the observed behaviour. Optically thin dust best accounts for the variability, where collisions drive dust production and destruction. Notably, the highest infrared variations are seen in systems that show Ca ii emission, supporting planetesimal collisions for all known debris discs, with the most energetic occurring in those with detected gaseous debris. The sample includes the only polluted white dwarf with a circumbinary disc, where the signal of the day–night cycle of its irradiated substellar companion appears diluted by dust emission.

scholarly journals Know thy star, know thy planet: chemo-kinematically characterizing TESS targets

2019 ◽  
Vol 491 (3) ◽  
pp. 4365-4381 ◽  
Author(s):  
Andreia Carrillo ◽  
Keith Hawkins ◽  
Brendan P Bowler ◽  
William Cochran ◽  
Andrew Vanderburg
Keyword(s):  
Distribution Functions ◽  
Target List ◽  
Thick Disc ◽  
Thin Disc ◽  
Candidate Target ◽  
Stellar Properties ◽  
The Individual ◽  
Host Stars ◽  
Gaia Dr2 ◽  
Kinematic Properties

ABSTRACT The Transiting Exoplanet Survey Satellite (TESS) has already begun to discover what will ultimately be thousands of exoplanets around nearby cool bright stars. These potential host stars must be well understood to accurately characterize exoplanets at the individual and population levels. We present a catalogue of the chemo-kinematic properties of 2218 434 stars in the TESS Candidate Target List using survey data from Gaia DR2, APOGEE, GALAH, RAVE, LAMOST, and photometrically derived stellar properties from SkyMapper. We compute kinematic thin disc, thick disc, and halo membership probabilities for these stars and find that though the majority of TESS targets are in the thin disc, 4 per cent of them reside in the thick disc and <1 per cent of them are in the halo. The TESS Objects of Interest in our sample also display similar contributions from the thin disc, thick disc, and halo with a majority of them being in the thin disc. We also explore metallicity and [α/Fe] distributions for each Galactic component and show that each cross-matched survey exhibits metallicity and [α/Fe] distribution functions that peak from higher to lower metallicity and lower to higher [α/Fe] from the thin disc to the halo. This catalogue will be useful to explore planet occurrence rates, among other things, with respect to kinematics, component membership, metallicity, or [α/Fe].

scholarly journals Planetary Messages in the Doppler Residuals

2004 ◽  
Vol 202 ◽  
pp. 20-28
Author(s):  
Geoffrey W. Marcy ◽  
Debra A. Fischer ◽  
R. Paul Butler ◽  
Steven S. Vogt
Keyword(s):  
Magnetic Fields ◽  
Time Scales ◽  
Extrasolar Planets ◽  
Velocity Fields ◽  
Occurrence Rate ◽  
High Occurrence ◽  
Magnetic Stars ◽  
Stellar Magnetic Fields ◽  
Host Stars

The Doppler residuals to the Keplerian fits for extrasolar planets reveal important properties of the planets and host stars. Stellar magnetic fields modify the photospheric velocity fields, causing Doppler fluctuations with unknown time scales. This Doppler “jitter”, seen prominently in the magnetic stars Epsilon Eridani and ξ Boo A, compromises the detectability of planets. The Doppler residuals during the transit of HD209458 reveal that the planet orbits in the same direction as the star spins. Moreover, the transit path across the star is nearly parallel to the stellar equator. Most interestingly, the Doppler residuals of known planets often reveal additional coherent variations, probably caused by additional companions. Both 55 Cancri and HD168443 reveal such coherent Doppler residuals. Another five planet–bearing stars observed at Lick show trends in the Doppler residuals indicating the presence of additional companions. Remarkably, about half of the known extrasolar planets reveal such coherent variations. This suggests that stars with planets have a high occurrence rate of harboring more distant companions, planetary or otherwise.

scholarly journals Flyby-induced misalignments in planet-hosting discs

2019 ◽  
Author(s):  
Rebecca Nealon ◽  
Nicolás Cuello ◽  
Richard Alexander
Keyword(s):  
Occurrence Rate ◽  
Protoplanetary Discs

Abstract We now have several observational examples of misaligned broken protoplanetary discs, where the disc inner regions are strongly misaligned with respect to the outer disc. Current models suggest that this disc structure can be generated with an internal misaligned companion (stellar or planetary), but the occurrence rate of these currently unobserved companions remains unknown. Here we explore whether a strong misalignment between the inner and outer disc can be formed without such a companion. We consider a disc that has an existing gap — essentially separating the disc into two regions — and use a flyby to disturb the discs, leading to a misalignment. Despite considering the most optimistic parameters for this scenario, we find maximum misalignments between the inner and outer disc of ∼45○ and that these misalignments are short-lived. We thus conclude that the currently observed misaligned discs must harbour internal, misaligned companions.

scholarly journals Dust clearing by radial drift in evolving protoplanetary discs

2020 ◽  
Vol 638 ◽  
pp. A156 ◽  
Author(s):  
Johan Appelgren ◽  
Michiel Lambrechts ◽  
Anders Johansen
Keyword(s):  
Accretion Rate ◽  
Stellar Mass ◽  
Dust Particles ◽  
Occurrence Rate ◽  
Linear Scaling ◽  
Streaming Instability ◽  
Dust Mass ◽  
Gas Accretion ◽  
Gas Ratio ◽  
Protoplanetary Discs

Recent surveys have revealed that protoplanetary discs typically have dust masses that appear to be insufficient to account for the high occurrence rate of exoplanet systems. We demonstrate that this observed dust depletion is consistent with the radial drift of pebbles. Using a Monte Carlo method we simulate the evolution of a cluster of protoplanetary discs using a 1D numerical method to viscously evolve each gas disc together with the radial drift of dust particles that have grown to 100 μm in size. For a 2 Myr-old cluster of stars, we find a slightly sublinear scaling between the gas disc mass and the gas accretion rate (Mg ∝ Ṁ0.9). However, for the dust mass we find that evolved dust discs have a much weaker scaling with the gas accretion rate, with the precise scaling depending on the age at which the cluster is sampled and the intrinsic age spread of the discs in the cluster. Ultimately, we find that the dust mass present in protoplanetary discs is on the order of 10–100 M⊕ in 1–3 Myr-old star-forming regions, a factor of 10–100 depleted from the original dust budget. As the dust drains from the outer disc, pebbles pile up in the inner disc and locally increase the dust-to-gas ratio by up to a factor of four above the initial value. In these regions of high dust-to-gas ratio we find conditions that are favourable for planetesimal formation via the streaming instability and subsequent growth by pebble accretion. We also find the following scaling relations with stellar mass within a 1–2 Myr-old cluster: a slightly super-linear scaling between the gas accretion rate and stellar mass (Ṁ ∝ M⋆1.4), a slightly super-linear scaling between the gas disc mass and the stellar mass (Mg ∝ M⋆1.4), and a super-linear relation between the dust disc mass and stellar mass (Md ∝ M⋆1.4−4.1).

scholarly journals Ground-Based Photometric Searches for Transiting Planets

2008 ◽  
Vol 4 (S253) ◽  
pp. 11-19
Author(s):  
Tsevi Mazeh
Keyword(s):  
Orbital Period ◽  
Selection Effect ◽  
Transiting Planets ◽  
Observational Selection ◽  
Planetary Mass ◽  
Photometric Observations

AbstractThis paper reviews the basic technical characteristics of the ground-based photometric searches for transiting planets, and discusses a possible observational selection effect. I suggest that additional photometric observations of the already observed fields might discover new transiting planets with periods around 4–6 days. The set of known transiting planets supports the intriguing correlation between the planetary mass and the orbital period suggested already in 2005.

A search for trends in spatially resolved debris discs at far-infrared wavelengths

2020 ◽  
Author(s):  
J P Marshall ◽  
L Wang ◽  
G M Kennedy ◽  
S T Zeegers ◽  
P Scicluna
Keyword(s):  
Scattered Light ◽  
Far Infrared ◽  
Building Blocks ◽  
Young Stars ◽  
Continuum Emission ◽  
Data Set ◽  
Spatially Resolved ◽  
Infrared Wavelengths ◽  
Host Stars ◽  
Protoplanetary Discs

Abstract Debris discs around main sequence stars are belts of planetesimals – asteroids and comets – formed in the protoplanetary discs around young stars. Planetesimals comprise both the building blocks of planets around young stars and the source of dusty debris around older stars. Imaging observations of dust continuum emission and scattered light reveals the location of these planetesimal belts around their host stars. Analysis of debris discs observed at millimetre wavelengths revealed a trend between the discs’ radii and the host star luminosities. This trend was tentatively linked to the preferential formation of dust-producing planetesimals near snow lines (specifically CO) in the protoplanetary discs around the host stars. Here we perform a homogeneous analysis of 96 debris discs observed at far-infrared wavelengths by the Herschel Space Observatory and fit the obtained distribution of radii and widths as a function of stellar luminosity with a power law relation. We identify a trend in disc radius as a function of stellar luminosity similar to that identified at millimetre wavelengths, but cannot convincingly recover it from the available data set due to the large uncertainties on disc radius and width inherent in the marginally spatially resolved data, and the bias of smaller discs around more distant stars (which are also the more luminous) being omitted from our analysis. We see a trend in disc temperature as a function of stellar luminosity, consistent with previous findings from similar analyses.

scholarly journals Spatial Orientations of Angular Momentum Vectors of Galaxies in Supercluster S [247+040+0029] and Substructures

2021 ◽  
Vol 7 (1) ◽  
pp. 39-48
Author(s):  
J. R. Malla ◽  
W. Saurer ◽  
B. Aryal
Keyword(s):  
Angular Momentum ◽  
Large Scale ◽  
Statistical Tests ◽  
Selection Effect ◽  
Simulation Method ◽  
Position Angle ◽  
Number Density ◽  
High Concentration ◽  
Chi Square ◽  
Isotropic Distribution

We present an analysis of spatial orientations of 1331 galaxies in the supercluster S [247+040+0029]. The main goal of this work is to search for a new substructure candidate and examine the orientation of angular momentum in the framework of three different scenarios (hierarchy, pancake, and primordial vorticity models) using “position angle-inclination method”, and to test the dependence on magnitude with the angular momentum orientations and their projections. We identified five substructures studying number density contour map with considerably high concentration of galaxies. Using random simulation method to remove the selection effect on database, we carried out expected isotropic distribution using cosmological principle. We then used three statistical tests: Chi-square, Auto-correlation, and Fourier to identify isotropy between observed and expected isotropic distributions. We varied radius in the range 0.3° to 1.0° to find substructures in supercluster. From this we found five sub-structures when taking radius 0.3° and two substructures for 1.0° radius in the number density counter maps of galaxies. By analyzing the result obtained through statistical tests, we are able to conform that evolution of galaxy in the supercluster and substructures supports “Hierarchy model" giving the angular momentum of galaxies in the large scale structure tends to be oriented random with respect to the reference coordinate system.

On the Inhomogeneity of Chemical Composition over the Surface of 21 Per

1976 ◽  
Vol 32 ◽  
pp. 343-349
Author(s):  
Yu.V. Glagolevsky ◽  
K.I. Kozlova ◽  
V.S. Lebedev ◽  
N.S. Polosukhina
Keyword(s):  
Chemical Composition ◽  
Spectral Line ◽  
Variable Star ◽  
Radial Velocities ◽  
Crimean Astrophysical Observatory ◽  
Line Intensities ◽  
Magnetic Variable

SummaryThe magnetic variable star 21 Per has been studied from 4 and 8 Å/mm spectra obtained with the 2.6 - meter reflector of the Crimean Astrophysical Observatory. Spectral line intensities (Wλ) and radial velocities (Vr) have been measured.

Production of New and Revised A.A.V.S.O. Charts

1979 ◽  
Vol 46 ◽  
pp. 368
Author(s):  
Clinton B. Ford
Keyword(s):  
Variable Star ◽  
Standard Form ◽  
Original Data ◽  
University Of Pennsylvania ◽  
Standard Format ◽  
Additional Information ◽  
The Gift ◽  
The University

A “new charts program” for the Americal Association of Variable Star Observers was instigated in 1966 via the gift to the Association of the complete variable star observing records, charts, photographs, etc. of the late Prof. Charles P. Olivier of the University of Pennsylvania (USA). Adequate material covering about 60 variables, not previously charted by the AAVSO, was included in this original data, and was suitably charted in reproducible standard format.Since 1966, much additional information has been assembled from other sources, three Catalogs have been issued which list the new or revised charts produced, and which specify how copies of same may be obtained. The latest such Catalog is dated June 1978, and lists 670 different charts covering a total of 611 variables none of which was charted in reproducible standard form previous to 1966.

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