| 1. |
- Akiyama, Eiji, et al.
(författare)
-
SPIRAL STRUCTURE AND DIFFERENTIAL DUST SIZE DISTRIBUTION IN THE LkH alpha 330 DISK
- 2016
-
Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 152:6
-
Tidskriftsartikel (refereegranskat)abstract
- Dust trapping accelerates the coagulation of dust particles, and, thus, it represents an initial step toward the formation of planetesimals. We report H-band (1.6 mu m) linear polarimetric observations and 0.87 mm interferometric continuum observations toward a transitional disk around LkH alpha 330. As a. result, a pair of spiral arms were detected in the H-band emission, and an asymmetric (potentially arm-like) structure was detected in the 0.87 mm continuum emission. We discuss the origin of the spiral arm and the asymmetric structure. and suggest that a massive unseen planet is the most plausible explanation. The possibility of dust trapping and grain growth causing the asymmetric structure was also investigated through the opacity index (beta) by plotting the observed spectral energy distribution slope between 0.87 mm from our Submillimeter Array observation and 1.3 mm from literature. The results imply that grains are indistinguishable from interstellar medium-like dust in the east side (beta = 2.0 +/- 0.5) but are much smaller in the west side beta = 0.7(-0.4)(+0.5), indicating differential dust size distribution between the two sides of the disk. Combining the results of near-infrared and submillimeter observations, we conjecture that the spiral arms exist at the upper surface and an asymmetric structure resides in the disk interior. Future observations at centimeter wavelengths and differential polarization imaging in other bands (Y-K) with extreme AO imagers are required to understand how large dust grains form and to further explore the dust distribution in the disk.
|
|
| 2. |
- Boccaletti, Anthony, et al.
(författare)
-
Fast-moving features in the debris disk around AU Microscopii
- 2015
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 526:7572, s. 230-
-
Tidskriftsartikel (refereegranskat)abstract
- In the 1980s, excess infrared emission was discovered around main-sequence stars; subsequent direct-imaging observations revealed orbiting disks of cold dust to be the source(1). These 'debris disks' were thought to be by-products of planet formation because they often exhibited morphological and brightness asymmetries that may result from gravitational perturbation by planets. This was proved to be true for the beta Pictoris system, in which the known planet generates an observable warp in the disk(2-5). The nearby, young, unusually active late-type star AU Microscopii hosts a well-studied edge-on debris disk; earlier observations in the visible and near-infrared found asymmetric localized structures in the form of intensity variations along the midplane of the disk beyond a distance of 20 astronomical units(6-9). Here we report high-contrast imaging that reveals a series of five large-scale features in the southeast side of the disk, at projected separations of 10-60 astronomical units, persisting over intervals of 1-4 years. All these features appear to move away from the star at projected speeds of 4-10 kilometres per second, suggesting highly eccentric or unbound trajectories if they are associated with physical entities. The origin, localization, morphology and rapid evolution of these features are difficult to reconcile with current theories.
|
|
| 3. |
- Calissendorff, Per, et al.
(författare)
-
The discrepancy between dynamical and theoretical mass in the triplet-system 2MASS J10364483+1521394
- 2017
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 604
-
Tidskriftsartikel (refereegranskat)abstract
- We combine new Lucky Imaging astrometry from New Technology Telescope /AstraLux Sur with already published astrometry from the AstraLux Large M-dwarf Multiplicity Survey to compute orbital elements and individual masses of the 2MASS J10364483 + 1521394 triple system belonging to the Ursa-Major moving group. The system consists of one primary low-mass M-dwarf orbited by two less massive companions, for which we determine a combined dynamical mass of MB+C = 0 : 48 +/- 0 : 14 M-circle dot. We show from the companions' relative motions that they are of equal mass (with a mass ratio of 1 : 00 +/- 0 : 03), thus 0 : 24 +/- 0 : 07 M-circle dot individually, with a separation of 3 : 2 +/- 0 : 3 AU, and we conclude that these masses are significantly higher (30%) than what is predicted by theoretical stellar evolutionary models. The biggest uncertainty remains the distance to the system, here adopted as 20 : 1 +/- 2 : 0 pc based on trigonometric parallax, whose ambiguity has a major impact on the result. With the new observational data we are able to conclude that the orbital period of the BC pair is 8.4(-0.021)(+0.04) yr.
|
|
| 4. |
- Calissendorff, Per, 1989-, et al.
(författare)
-
Updated orbital monitoring and dynamical masses for nearby M-dwarf binaries
- 2022
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
-
Tidskriftsartikel (refereegranskat)abstract
- Young M-type binaries are particularly useful for precise isochronal dating by taking advantage of their extended pre-main sequence evolution. Orbital monitoring of these low-mass objects becomes essential in constraining their fundamental properties, as dynamical masses can be extracted from their Keplerian motion. Here, we present the combined efforts of the AstraLux Large Multiplicity Survey, together with a filler sub-programme from the SpHere INfrared Exoplanet (SHINE) project and previously unpublished data from the FastCam lucky imaging camera at the Nordical Optical Telescope (NOT) and the NaCo instrument at the Very Large Telescope (VLT). Building on previous work, we use archival and new astrometric data to constrain orbital parameters for 20 M-type binaries. We identify that eight of the binaries have strong Bayesian probabilities and belong to known young moving groups (YMGs). We provide a first attempt at constraining orbital parameters for 14 of the binaries in our sample, with the remaining six having previously fitted orbits for which we provide additional astrometric data and updated Gaia parallaxes. The substantial orbital information built up here for four of the binaries allows for direct comparison between individual dynamical masses and theoretical masses from stellar evolutionary model isochrones, with an additional three binary systems with tentative individual dynamical mass estimates likely to be improved in the near future. We attained an overall agreement between the dynamical masses and the theoretical masses from the isochrones based on the assumed YMG age of the respective binary pair. The two systems with the best orbital constrains for which we obtained individual dynamical masses, J0728 and J2317, display higher dynamical masses than predicted by evolutionary models.
|
|
| 5. |
- Cataldi, Gianni, et al.
(författare)
-
Primordial or Secondary? Testing Models of Debris Disk Gas with ALMA*
- 2023
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 951:2
-
Tidskriftsartikel (refereegranskat)abstract
- The origin and evolution of gas in debris disks are still not well understood. Secondary gas production from cometary material or a primordial origin have been proposed. So far, observations have mostly concentrated on CO, with only a few C observations available. We overview the C and CO content of debris disk gas and test state-of-the-art models. We use new and archival Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO and C i emission, complemented by C ii data from Herschel, for a sample of 14 debris disks. This expands the number of disks with ALMA measurements of both CO and C i by 10 disks. We present new detections of C i emission toward three disks: HD 21997, HD 121191, and HD 121617. We use a simple disk model to derive gas masses and column densities. We find that current state-of-the-art models of secondary gas production overpredict the C-0 content of debris disk gas. This does not rule out a secondary origin, but might indicate that the models require an additional C removal process. Alternatively, the gas might be produced in transient events rather than a steady-state collisional cascade. We also test a primordial gas origin by comparing our results to a simplified thermochemical model. This yields promising results, but more detailed work is required before a conclusion can be reached. Our work demonstrates that the combination of C and CO data is a powerful tool to advance our understanding of debris disk gas.
|
|
| 6. |
- Cataldi, Gianni, et al.
(författare)
-
The Surprisingly Low Carbon Mass in the Debris Disk around HD 32297
- 2020
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 892:2
-
Tidskriftsartikel (refereegranskat)abstract
- Gas has been detected in a number of debris disks. It is likely secondary, i.e., produced by colliding solids. Here, we report ALMA Band 8 observations of neutral carbon in the CO-rich debris disk around the 15-30 Myr old A-type star HD 32297. We find that C-0 is located in a ring at similar to 110 au with an FWHM of similar to 80 au and has a mass of (3.5 0.2) x 10(-3) M-circle plus. Naively, such a surprisingly small mass can be accumulated from CO photodissociation in a time as short as similar to 10(4) yr. We develop a simple model for gas production and destruction in this system, properly accounting for CO self-shielding and shielding by neutral carbon, and introducing a removal mechanism for carbon gas. We find that the most likely scenario to explain both C-0 and CO observations is one where the carbon gas is rapidly removed on a timescale of order a thousand years and the system maintains a very high CO production rate of similar to 15 M-circle plus Myr(-1), much higher than the rate of dust grind-down. We propose a possible scenario to meet these peculiar conditions: the capture of carbon onto dust grains, followed by rapid CO re-formation and rerelease. In steady state, CO would continuously be recycled, producing a CO-rich gas ring that shows no appreciable spreading over time. This picture might be extended to explain other gas-rich debris disks.
|
|
| 7. |
- Currie, Thayne, et al.
(författare)
-
RECOVERY OF THE CANDIDATE PROTOPLANET HD 100546 b WITH GEMINI/NICI AND DETECTION OF ADDITIONAL (PLANET-INDUCED ?) DISK STRUCTURE AT SMALL SEPARATIONS
- 2014
-
Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 796:2, s. L30-
-
Tidskriftsartikel (refereegranskat)abstract
- We report the first independent, second epoch (re-) detection of a directly imaged protoplanet candidate. Using L' high-contrast imaging of HD 100546 taken with the Near-Infrared Coronagraph and Imager on Gemini South, we recover HD 100546 b with a position and brightness consistent with the original Very Large Telescope/NAos-COnica detection from Quanz et al., although data obtained after 2013 will be required to decisively demonstrate common proper motion. HD 100546 b may be spatially resolved, up to approximate to 12-13 AU in diameter, and is embedded in a finger of thermal IR-bright, polarized emission extending inward to at least 0 ''.3. Standard hot-start models imply a mass of approximate to 15 M-J. However, if HD 100546 b is newly formed or made visible by a circumplanetary disk, both of which are plausible, its mass is significantly lower (e.g., 1-7 M-J). Additionally, we discover a thermal IR-bright disk feature, possibly a spiral density wave, at roughly the same angular separation as HD 100546 b but 90 degrees. away. Our interpretation of this feature as a spiral arm is not decisive, but modeling analyses using spiral density wave theory implies a wave launching point exterior to approximate to 0 ''.45 embedded within the visible disk structure: plausibly evidence for a second, hitherto unseen, wide-separation planet. With one confirmed protoplanet candidate and evidence for one to two others, HD 100546 is an important evolutionary precursor to intermediate-mass stars with multiple super-Jovian planets at moderate/wide separations like HR 8799.
|
|
| 8. |
- de Leon, Jerome, et al.
(författare)
-
NEAR-IR HIGH-RESOLUTION IMAGING POLARIMETRY OF THE SU Aur DISK : CLUES FOR TIDAL TAILS?
- 2015
-
Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 806:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present new high-resolution (similar to 0.09) H-band imaging observations of the circumstellar disk around the T Tauri star SU Aur. Our observations with Subaru-HiCIAO have revealed the presence of scattered light as close as 0.15 (similar to 20 AU) to the star. Within our image, we identify bright emission associated with a disk with a minimum radius of similar to 90 AU, an inclination of similar to 35 degrees from the plane of the sky, and an approximate PA of 15 degrees for the major axis. We find a brightness asymmetry between the northern and southern sides of the disk due to a non-axisymmetric disk structure. We also identify a pair of asymmetric tail structures extending east and west from the disk. The western tail extends at least 2.5 (350 AU) from the star, and is probably associated with a reflection nebula previously observed at optical and near-IR wavelengths. The eastern tail extends at least 1. (140 AU) at the present signal-to-noise. These tails are likely due to an encounter with an unseen brown dwarf, but our results do not exclude the explanation that these tails are outflow cavities or jets.
|
|
| 9. |
- Durkan, Stephen, et al.
(författare)
-
Radial velocity survey of spatially resolved young, low-mass binaries
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 618
-
Tidskriftsartikel (refereegranskat)abstract
- The identification and characterisation of low-mass binaries is of importance for a range of astrophysical investigations. Low-mass binaries in young (similar to 10-100 Myr) moving groups (YMGs) in the solar neighborhood are of particular significance as they provide unique opportunities to calibrate stellar models and evaluate the ages and coevality of the groups themselves. Low-mass M-dwarfs have pre-main sequence life times on the order of similar to 100 Myr and therefore are continually evolving along a mass-luminosity track throughout the YMG phase, providing ideal laboratories for precise isochronal dating, if a model-independent dynamical mass can be measured. AstraLux lucky imaging multiplicity surveys have recently identified hundreds of new YMG low-mass binaries, where a subsample of M-dwarf multiples have estimated orbital periods less than 50 yr. We have conducted a radial velocity survey of a sample of 29 such targets to complement the astrometric data. This will allow enhanced orbital determinations and precise dynamical masses to be derived in a shorter timeframe than possible with astrometric monitoring alone, and allow for a more reliable isochronal analysis. Here we present radial velocity measurements derived for our sample over several epochs. We report the detection of the three-component spectroscopic multiple 2MASS J05301858-5358483, for which the C component is a new discovery, and forms a tight pair with the B component. Originally identified as a YMG member, we find that this system is a likely old field interloper, whose high chromospheric activity level is caused by tidal spin-up of the tight BC pair. Two other triple systems with a tight pair exist in the sample, 2MASS J04244260-0647313 (previously known) and 2MASS J20163382-0711456, but for the rest of the targets we find that additional tidally synchronized companions are highly unlikely, providing further evidence that their high chromospheric activity levels are generally signatures of youth.
|
|
| 10. |
- Follette, Katherine B., et al.
(författare)
-
SEEDS ADAPTIVE OPTICS IMAGING OF THE ASYMMETRIC TRANSITION DISK OPH IRS 48 IN SCATTERED LIGHT
- 2015
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 798:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present the first resolved near-infrared imagery of the transition disk Oph IRS 48 (WLY 2-48), which was recently observed with ALMA to have a strongly asymmetric submillimeter flux distribution. H-band polarized intensity images show a similar to 60 AU radius scattered light cavity with two pronounced arcs of emission, one from northeast to southeast and one smaller, fainter, and more distant arc in the northwest. K-band scattered light imagery reveals a similar morphology, but with a clear third arc along the southwestern rim of the disk cavity. This arc meets the northwestern arc at nearly a right angle, revealing the presence of a spiral arm or local surface brightness deficit in the disk, and explaining the east-west brightness asymmetry in the H-band data. We also present 0.8-5.4 mu m IRTF SpeX spectra of this object, which allow us to constrain the spectral class to A0 +/- 1 and measure a low mass accretion rate of 10(-8.5) M-circle dot yr(-1), both consistent with previous estimates. We investigate a variety of reddening laws in order to fit the multiwavelength spectral energy distribution of Oph IRS 48 and find a best fit consistent with a younger, higher luminosity star than previous estimates.
|
|
