Trends in Silicates in the β Pictoris Disk Lu, Cicero X.; Chen, Christine H.; Sargent, B. A. ...
Astrophysical journal/The Astrophysical journal,
07/2022, Letnik:
933, Številka:
1
Journal Article
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Abstract
While
β
Pic is known to host silicates in ring-like structures, whether the properties of these silicate dust vary with stellocentric distance remains an open question. We re-analyze the
β
...Pictoris debris disk spectrum from the Spitzer Infrared Spectrograph (IRS) and a new Infrared Telescope Facility Spectrograph and Imager spectrum to investigate trends in Fe/Mg ratio, shape, and crystallinity in grains as a function of wavelength, a proxy for stellocentric distance. By analyzing a re-calibrated and re-extracted spectrum, we identify a new 18
μ
m forsterite emission feature and recover a 23
μ
m forsterite emission feature with a substantially larger line-to-continuum ratio than previously reported. We find that these prominent spectral features are primarily produced by small submicron-sized grains, which are continuously generated and replenished from planetesimal collisions in the disk and can elucidate their parent bodies’ composition. We discover three trends about these small grains: as stellocentric distance increases, (1) small silicate grains become more crystalline (less amorphous), (2) they become more irregular in shape, and (3) for crystalline silicate grains, the Fe/Mg ratio decreases. Applying these trends to
β
Pic’s planetary architecture, we find that the dust population exterior to the orbits of
β
Pic b and c differs substantially in crystallinity and shape. We also find a tentative 3–5
μ
m dust excess due to spatially unresolved hot dust emission close to the star. From our findings, we infer that the surfaces of large planetesimals are more Fe-rich and collisionally processed closer to the star but more Fe-poor and primordial farther from the star.
Large Interferometer For Exoplanets (LIFE) Carrión-González, Óscar; Kammerer, Jens; Angerhausen, Daniel ...
Astronomy and astrophysics (Berlin),
10/2023, Letnik:
678
Journal Article, Web Resource
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Context.
The next generation of space-based observatories will characterize the atmospheres of low-mass, temperate exoplanets with the direct-imaging technique. This will be a major step forward in ...our understanding of exoplanet diversity and the prevalence of potentially habitable conditions beyond the Earth.
Aims.
We compute a list of currently known exoplanets detectable with the mid-infrared Large Interferometer For Exoplanets (LIFE) in thermal emission. We also compute the list of known exoplanets accessible to a notional design of the future Habitable Worlds Observatory (HWO), observing in reflected starlight.
Methods.
With a pre-existing statistical methodology, we processed the NASA Exoplanet Archive and computed orbital realizations for each known exoplanet. We derived their mass, radius, equilibrium temperature, and planet-star angular separation. We used the LIFEsim simulator to compute the integration time (
t
int
) required to detect each planet with LIFE. A planet is considered detectable if a broadband signal-to-noise ratio
S
/
N
= 7 is achieved over the spectral range 4–18.5 µm in
t
int
< 100 h. We tested whether the planet is accessible to HWO in reflected starlight based on its notional inner and outer working angles, and minimum planet-to-star contrast.
Results.
LIFE's reference configuration (four 2-m telescopes with 5% throughput and a nulling baseline between 10–100 m) can detect 212 known exoplanets within 20 pc. Of these, 49 are also accessible to HWO in reflected starlight, offering a unique opportunity for synergies in atmospheric characterization. LIFE can also detect 32 known transiting exoplanets. Furthermore, we find 38 LIFE-detectable planets orbiting in the habitable zone, of which 13 have
M
p
< 5
M
⊕
and eight have 5
M
⊕
<
M
p
< 10
M
⊕
.
Conclusions.
LIFE already has enough targets to perform ground-breaking analyses of low-mass, habitable-zone exoplanets, a fraction of which will also be accessible to other instruments.
ABSTRACT
We present polarized light observations of the transitional disc around Sz 91 acquired with VLT/NaCo at H (1.7μm) and Ks (2.2μm) bands. We resolve the disc and detect polarized emission up ...to ∼0.5 arcsec (∼80 au) along with a central cavity at both bands. We computed a radiative transfer model that accounts for the main characteristics of the polarized observations. We found that the emission is best explained by small, porous grains distributed in a disc with a ∼45 au cavity. Previous ALMA observations have revealed a large sub-mm cavity (∼83 au) and extended gas emission from the innermost (<16 au) regions up to almost 400 au from the star. Dynamical clearing by multiple low-mass planets arises as the most probable mechanism for the origin of Sz 91’s peculiar structure. Using new L′-band ADI observations, we can rule out companions more massive than Mp ≥ 8 MJup beyond 45 au assuming hot-start models. The disc is clearly asymmetric in polarized light along the minor axis, with the north side brighter than the south side. Differences in position angle between the disc observed at sub-mm wavelengths with ALMA and our NaCo observations were found. This suggests that the disc around Sz 91 could be highly structured. Higher signal-to-noise near-IR and sub-mm observations are needed to confirm the existence of such structures and to improve the current understanding of the origin of transitional discs.
Stellar multiplicity properties have been studied for the lowest and the highest stellar masses, but intermediate-mass stars from F-type to late A-type have received relatively little attention. ...Here, we report on a Gemini/NICI snapshot imaging survey of 138 such stars in the young Scorpius-Centaurus (Sco-Cen) region, for the purpose of studying multiplicity with sensitivity down to planetary masses at wide separations. In addition to two brown dwarfs and a companion straddling the hydrogen-burning limit which we reported previously, here we present 26 new stellar companions and determine a multiplicity fraction within 0".1-5".0 of 21% + or - 4%. Depending on the adopted semimajor axis distribution, our results imply a total multiplicity in the range of ~60%-80%, which further supports the known trend of a smooth continuous increase in the multiplicity fraction as a function of primary stellar mass. A surprising feature in the sample is a distinct lack of nearly equal-mass binaries, for which we discuss possible reasons. The survey yielded no additional companions below or near the deuterium-burning limit, implying that their frequency at >200 AU separations is not quite as high as might be inferred from previous detections of such objects within the Sco-Cen region.
Abstract The JWST NIRSpec integral field unit (IFU) presents a unique opportunity to observe directly imaged exoplanets from 3 to 5 μ m at moderate spectral resolution ( R ∼ 2700) and thereby better ...constrain the composition, disequilibrium chemistry, and cloud properties of their atmospheres. In this work, we present the first NIRSpec IFU high-contrast observations of a substellar companion that requires starlight suppression techniques. We develop specific data-reduction strategies to study faint companions around bright stars and assess the performance of NIRSpec at high contrast. First, we demonstrate an approach to forward model the companion signal and the starlight directly in the detector images, which mitigates the effects of NIRSpec’s spatial undersampling. We demonstrate a sensitivity to planets that are 3 × 10 −6 fainter than their stars at 1″, or 3 × 10 −5 at 0.″3. Then, we implement a reference star point-spread function subtraction and a spectral extraction that does not require spatially and spectrally regularly sampled spectral cubes. This allows us to extract a moderate resolution ( R ∼ 2,700) spectrum of the faint T dwarf companion HD 19467 B from 2.9 to 5.2 μ m with a signal-to-noise ratio of ∼10 per resolution element. Across this wavelength range, HD 19467 B has a flux ratio varying between 10 −5 and 10 −4 and a separation relative to its star of 1.″6. A companion paper by Hoch et al. more deeply analyzes the atmospheric properties of this companion based on the extracted spectrum. Using the methods developed here, NIRSpec’s sensitivity may enable direct detection and spectral characterization of relatively old (∼1 Gyr), cool (∼250 K), and closely separated (∼3–5 au) exoplanets that are less massive than Jupiter.
Abstract
The
direct
characterization of exoplanetary systems with high-contrast imaging is among the highest priorities for the broader exoplanet community. As large space missions will be necessary ...for detecting and characterizing exo-Earth twins, developing the techniques and technology for direct imaging of exoplanets is a driving focus for the community. For the first time, JWST will directly observe extrasolar planets at mid-infrared wavelengths beyond 5
μ
m, deliver detailed spectroscopy revealing much more precise chemical abundances and atmospheric conditions, and provide sensitivity to analogs of our solar system ice-giant planets at wide orbital separations, an entirely new class of exoplanet. However, in order to maximize the scientific output over the lifetime of the mission, an exquisite understanding of the instrumental performance of JWST is needed as early in the mission as possible. In this paper, we describe our 55 hr Early Release Science Program that will utilize all four JWST instruments to extend the characterization of planetary-mass companions to ∼15
μ
m as well as image a circumstellar disk in the mid-infrared with unprecedented sensitivity. Our program will also assess the performance of the observatory in the key modes expected to be commonly used for exoplanet direct imaging and spectroscopy, optimize data calibration and processing, and generate representative data sets that will enable a broad user base to effectively plan for general observing programs in future Cycles.
We report on a search for low mass companions within 10 AU of the star Fomalhaut, using narrowband observations at 4.05 mu m obtained with the Apodizing Phase Plate coronagraph on the VLT/NaCo. Our ...observations place a model-dependent upper mass limit of 12-20 M sub(jup) from 4 to 10 AU, covering the semimajor axis search space between interferometric imaging measurements and other direct imaging non-detections. These observations rule out models where the large semimajor axis for the putative candidate companion Fomalhaut b is explained by dynamical scattering from a more massive companion in the inner stellar system, where such giant planets are thought to form.
Abstract
We conducted a 12-month monitoring campaign of 33 T Tauri stars (TTS) in Taurus. Our goal was to monitor objects that possess a disc but have a weak H α line, a common accretion tracer for ...young stars, in order to determine whether they host a passive circumstellar disc. We used medium-resolution optical spectroscopy to assess the accretion status of the objects and to measure the H α line. We found no convincing examples of passive discs: only transition disc and debris disc systems in our sample are non-accreting. Among accretors, we found no example of flickering accretion, leading to an upper limit of 2.2 per cent on the duty cycle of accretion gaps, assuming that all accreting TTS experience such events. When combining literature results with our observations, we found that the reliability of traditional H α-based criteria to test for accretion is high but imperfect, particularly for low-mass TTS. We found a significant correlation between stellar mass and the full width at 10 per cent of the peak (W10) of the H α line that does not seem to be related to variations in free-fall velocity. Finally, our data revealed a positive correlation between the H α equivalent width and its W10, indicative of a systematic modulation in the line profile whereby the high-velocity wings of the line are proportionally more enhanced than its core when the line luminosity increases. We argue that this supports the hypothesis that the mass accretion rate on the central star is correlated with the H α W10 through a common physical mechanism.
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