Publications
65 results found
Jankovic MR, Owen JE, Mohanty S, 2019, Close-in super-Earths: The first and the last stages of planet formation in an MRI-accreting disc, Monthly Notices of the Royal Astronomical Society, Vol: 484, Pages: 2296-2308, ISSN: 0035-8711
We explore in situ formation and subsequent evolution of close-in super-Earths and mini-Neptunes. We adopt a steady-state inner protoplanetary gas disc structure that arises from viscous accretion due to the magneto-rotational instability (MRI). We consider the evolution of dust in the inner disc, including growth, radial drift, and fragmentation, and find that dust particles that radially drift into the inner disc fragment severely due to the MRI-induced turbulence. This result has two consequences: (1) radial drift of grains within the inner disc is quenched, leading to an enhancement of dust in the inner regions that scales as dust-to-gas-mass-flux-ratio at ∼1 au; (2) however, despite this enhancement, planetesimal formation is impeded by the small grain size. Nevertheless, assuming that planetary cores are present in the inner disc, we then investigate the accretion of atmospheres on to cores and their subsequent photoevaporation. We then compare our results to the observed exoplanet mass–radius relationship. We find that (1) the low gas surface densities and high temperatures in the inner disc reduce gas accretion on to cores compared to the minimum mass solar nebula, preventing the cores from growing into hot Jupiters, in agreement with the data; (2) however, our predicted envelope masses are still typically larger than observed ones. Finally, we sketch a qualitative picture of how grains may grow and planetesimals form in the inner disc if grain effects on the ionization levels and the MRI and the back reaction of the dust on the gas (both neglected in our calculations) are accounted for.
Jankovic MR, Haworth TJ, Ilee JD, et al., 2019, Observing substructure in circumstellar discs around massive young stellar objects, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 482, Pages: 4673-4686, ISSN: 0035-8711
Mohanty S, Jankovic MR, Tan JC, et al., 2018, Inside-out planet formation. V. structure of the inner disk as implied by the MRI, Astrophysical Journal, Vol: 861, Pages: 1-27, ISSN: 0004-637X
The large population of Earth to super-Earth sized planets found very closeto their host stars has motivated consideration of $in$ $situ$ formationmodels. In particular, Inside-Out Planet Formation is a scenario in whichplanets coalesce sequentially in the disk, at the local gas pressure maximumnear the inner boundary of the dead zone. The pressure maximum arises from adecline in viscosity, going from the active innermost disk (where thermalionization of alkalis yields high viscosities via the magneto-rotationalinstability (MRI)) to the adjacent dead zone (where the MRI is quenched).Previous studies of the pressure maximum, based on $\alpha$-disk models, haveassumed ad hoc values for the viscosity parameter $\alpha$ in the active zone,ignoring the detailed physics of the MRI. Here we explicitly couple the MRIcriteria to the $\alpha$-disk equations, to find steady-state (constantaccretion rate) solutions for the disk structure. We consider the effects ofboth Ohmic and ambipolar resistivities, and find solutions for a range of diskaccretion rates ($\dot{M}$ = $10^{-10}$ - $10^{-8}$ ${\rm M}_{\odot}$/yr),stellar masses ($M_{\ast}$ = 0.1 - 1 ${\rm M}_{\odot}$), and fiducial values ofthe $non$-MRI $\alpha$-viscosity in the dead zone ($\alpha_{\rm {DZ}} =10^{-5}$ - $10^{-3}$). We find that: (1) A midplane pressure maximum formsradially $outside$ the inner boundary of the dead zone; (2) Hall resistivitydominates near the midplane in the inner disk, which may explain why close-inplanets do $not$ form in $\sim$50% of systems; (3) X-ray ionization can becompetitive with thermal ionization in the inner disk, because of the lowsurface density there in steady-state; and (4) our inner disk solutions areviscously unstable to surface density perturbations.
Hu X, Tan JC, Zhu Z, et al., 2018, Inside-out planet formation. IV. Pebble evolution and planet formation timescales, Astrophysical Journal, Vol: 857, ISSN: 0004-637X
Systems with tightly packed inner planets (STIPs) are very common. Chatterjee & Tan proposed Inside-out Planet Formation (IOPF), an in situ formation theory, to explain these planets. IOPF involves sequential planet formation from pebble-rich rings that are fed from the outer disk and trapped at the pressure maximum associated with the dead zone inner boundary (DZIB). Planet masses are set by their ability to open a gap and cause the DZIB to retreat outwards. We present models for the disk density and temperature structures that are relevant to the conditions of IOPF. For a wide range of DZIB conditions, we evaluate the gap-opening masses of planets in these disks that are expected to lead to the truncation of pebble accretion onto the forming planet. We then consider the evolution of dust and pebbles in the disk, estimating that pebbles typically grow to sizes of a few centimeters during their radial drift from several tens of astronomical units to the inner, lesssim1 au scale disk. A large fraction of the accretion flux of solids is expected to be in such pebbles. This allows us to estimate the timescales for individual planet formation and the entire planetary system formation in the IOPF scenario. We find that to produce realistic STIPs within reasonable timescales similar to disk lifetimes requires disk accretion rates of ~10−9 M ⊙ yr−1 and relatively low viscosity conditions in the DZIB region, i.e., a Shakura–Sunyaev parameter of α ~ 10−4.
Haworth TJ, Facchini S, Clarke CJ, et al., 2018, Where can a Trappist-1 planetary system be produced?, Monthly Notices of the Royal Astronomical Society, Vol: 475, Pages: 5460-5473, ISSN: 0035-8711
We study the evolution of protoplanetary discs that would have been precursors of a Trappist-1-like system under the action of accretion and external photoevaporation in different radiation environments. Dust grains swiftly grow above the critical size below which they are entrained in the photoevaporative wind, so although gas is continually depleted, dust is resilient to photoevaporation after only a short time. This means that the ratio of the mass in solids (dust plus planetary) to the mass in gas rises steadily over time. Dust is still stripped early on, and the initial disc mass required to produce the observed 4 M⊕ of Trappist-1 planets is high. For example, assuming a Fatuzzo & Adams distribution of UV fields, typical initial disc masses have to be >30 per cent the stellar (which are still Toomre Q stable) for the majority of similar mass M dwarfs to be viable hosts of the Trappist-1 planets. Even in the case of the lowest UV environments observed, there is a strong loss of dust due to photoevaporation at early times from the weakly bound outer regions of the disc. This minimum level of dust loss is a factor of 2 higher than that which would be lost by accretion on to the star during 10 Myr of evolution. Consequently, even in these least irradiated environments, discs that are viable Trappist-1 precursors need to be initially massive (>10 per cent of the stellar mass).
Haworth TJ, Booth RA, Homan W, et al., 2017, Radiation-pressure-driven sub-Keplerian rotation of the disc around the AGB star L2 Pup, Monthly Notices of the Royal Astronomical Society, Vol: 473, Pages: 317-327, ISSN: 0035-8711
We study the sub-Keplerian rotation and dust content of the circumstellar material around the asymptotic giant branch (AGB) star L2 Puppis. We find that the thermal pressure gradient alone cannot explain the observed rotation profile. We find that there is a family of possible dust populations for which radiation pressure can drive the observed sub-Keplerian rotation. This set of solutions is further constrained by the spectral energy distribution (SED) of the system, and we find that a dust-to-gas mass ratio of ∼10−3 and a maximum grain size that decreases radially outwards can satisfy both the rotation curve and SED. These dust populations are dynamically tightly coupled to the gas azimuthally. However, grains larger than ∼ 0.5 μm are driven outwards radially by radiation pressure at velocities ∼5 km s−1, which implies a dust replenishment rate of ∼3 × 10−9 M⊙ yr−1. This replenishment rate is consistent with observational estimates to within uncertainties. Coupling between the radial motion of the dust and gas is weak and hence the gas does not share in this rapid outward motion. Overall, we conclude that radiation pressure is a capable and necessary mechanism to explain the observed rotation profile of L2 Pup, and offers other additional constraints on the dust properties.
Mulders GD, Pascucci I, Manara CF, et al., 2017, Constraints from dust mass and mass accretion rate measurements on angular momentum transport in protoplanetary disks, Astrophysical Journal, Vol: 847, ISSN: 0004-637X
In this paper, we investigate the relation between disk mass and mass accretion rate to constrain the mechanism ofangular momentum transport in protoplanetary disks. We find a correlation between dust disk mass and mass accretionrate in Chamaeleon I with a slope that is close to linear, similar to the one recently identified in Lupus. We investigatethe effect of stellar mass and find that the intrinsic scatter around the best-fit Mdust–M and M˙ acc–M relations isuncorrelated. We simulate synthetic observations of an ensemble of evolving disks using a Monte Carlo approach andfind that disks with a constant α viscosity can fit the observed relations between dust mass, mass accretion rate, andstellar mass but overpredict the strength of the correlation between disk mass and mass accretion rate when usingstandard initial conditions. We find two possible solutions. In the first one, the observed scatter in Mdust and M˙ acc is notprimordial, but arises from additional physical processes or uncertainties in estimating the disk gas mass. Most likelygrain growth and radial drift affect the observable dust mass, while variability on large timescales affects the massaccretion rates. In the second scenario, the observed scatter is primordial, but disks have not evolved substantially at theage of Lupus and Chamaeleon I owing to a low viscosity or a large initial disk radius. More accurate estimates of thedisk mass and gas disk sizes in a large sample of protoplanetary disks, through either direct observations of the gas orspatially resolved multiwavelength observations of the dust with ALMA, are needed to discriminate between bothscenarios or to constrain alternative angular momentum transport mechanisms such as MHD disk wi
Manara CF, Testi L, Herczeg GJ, et al., 2017, X-shooter study of accretion in Chamaeleon I: II. A steeper increase of accretion with stellar mass for very low-mass stars?, Astronomy and Astrophysics, Vol: 604, ISSN: 0004-6361
The dependence of the mass accretion rate on the stellar properties is a key constraint for star formation and disk evolution studies. Here we present a study of a sample of stars in the Chamaeleon I star-forming region carried out using spectra taken with the ESO VLT/X-shooter spectrograph. The sample is nearly complete down to stellar masses (M⋆) ~0.1 M⊙ for the young stars still harboring a disk in this region. We derive the stellar and accretion parameters using a self-consistent method to fit the broadband flux-calibrated medium resolution spectrum. The correlation between accretion luminosity to stellar luminosity, and of mass accretion rate to stellar mass in the logarithmic plane yields slopes of 1.9 ± 0.1 and 2.3 ± 0.3, respectively. These slopes and the accretion rates are consistent with previous results in various star-forming regions and with different theoretical frameworks. However, we find that a broken power-law fit, with a steeper slope for stellar luminosity lower than ~0.45 L⊙ and for stellar masses lower than ~0.3 M⊙ is slightly preferred according to different statistical tests, but the single power-law model is not excluded. The steeper relation for lower mass stars can be interpreted as a faster evolution in the past for accretion in disks around these objects, or as different accretion regimes in different stellar mass ranges. Finally, we find two regions on the mass accretion versus stellar mass plane that are empty of objects: one region at high mass accretion rates and low stellar masses, which is related to the steeper dependence of the two parameters we derived. The second region is located just above the observational limits imposed by chromospheric emission, at M⋆ ~ 0.3 − 0.4 M⊙. These are typical masses where photoevaporation is known to be effective. The mass accretion rates of this region are ~10-10M⊙/yr, which is compatible with the value expected for photoevaporation to rapidly dissipate the inner disk.
Long F, Herczeg GJ, Pascucci I, et al., 2017, An ALMA survey of CO isotopologue emission from protoplanetary disks in Chamaeleon I, Astrophysical Journal, Vol: 844, ISSN: 0004-637X
The mass of a protoplanetary disk limits the formation and future growth of any planet. Masses of protoplanetary disks are usually calculated from measurements of the dust continuum emission by assuming an interstellar gas-to-dust ratio. To investigate the utility of CO as an alternate probe of disk mass, we use ALMA to survey ¹³CO and C¹⁸O J = 3–2 line emission from a sample of 93 protoplanetary disks around stars and brown dwarfs with masses from in the nearby Chamaeleon I star-forming region. We detect ¹³CO emission from 17 sources and C¹⁸O from only one source. Gas masses for disks are then estimated by comparing the CO line luminosities to results from published disk models that include CO freeze-out and isotope-selective photodissociation. Under the assumption of a typical interstellar medium CO-to-H₂ ratio of 10−⁴, the resulting gas masses are implausibly low, with an average gas mass of ~0.05 M Jup as inferred from the average flux of stacked ¹³CO lines. The low gas masses and gas-to-dust ratios for Cha I disks are both consistent with similar results from disks in the Lupus star-forming region. The faint CO line emission may instead be explained if disks have much higher gas masses, but freeze-out of CO or complex C-bearing molecules is underestimated in disk models. The conversion of CO flux to CO gas mass also suffers from uncertainties in disk structures, which could affect gas temperatures. CO emission lines will only be a good tracer of the disk mass when models for C and CO depletion are confirmed to be accurate.
Ricci L, Cazzoletti P, Czekala I, et al., 2017, ALMA observations of the young substellar binary System 2M1207, Astronomical Journal, Vol: 154, ISSN: 0004-6256
We present ALMA observations of the 2M1207 system, a young binary made of a brown dwarf with a planetarymasscompanion at a projected separation of about 40 au. We detect emission from dust continuum at 0.89 mm andfrom the J = 3 - 2 rotational transition of CO from a very compact disk around the young brown dwarf. Thesmall radius found for this brown dwarf disk may be due to truncation from the tidal interaction with the planetarymasscompanion. Under the assumption of optically thin dust emission, we estimate a dust mass of 0.1 M⊕ for the2M1207A disk and a 3σ upper limit of ∼1 MMoon for dust surrounding 2M1207b, which is the tightest upper limitobtained so far for the mass of dust particles surrounding a young planetary-mass companion. We discuss theimpact of this and other non-detections of young planetary-mass companions for models of planet formationthat predict circumplanetary material to surround these objects.
Drabek-Maunder E, Mohanty S, Greaves J, et al., 2016, HCO+ Detection of dust-depleted gas in the inner hole of the LkCa 15 pre-transitional disk, The Astrophysical Journal, Vol: 833, ISSN: 0004-637X
LkCa 15 is an extensively studied star in the Taurus region, known for its pre-transitional disk with a large inner cavity in the dust continuum and normal gas accretion rate. The most popular hypothesis to explain the LkCa 15 data invokes one or more planets to carve out the inner cavity, while gas continues to flow across the gap from the outer disk onto the central star. We present spatially unresolved HCO+ $J=4\to 3$ observations of the LkCa 15 disk from the James Clerk Maxwell telescope (JCMT) and model the data with the ProDiMo code. We find that: (1) HCO+ line-wings are clearly detected, certifying the presence of gas in the cavity within lesssim50 au of the star. (2) Reproducing the observed line-wing flux requires both a significant suppression of cavity dust (by a factor gsim104 compared to the interstellar medium (ISM)) and a substantial increase in the gas scale-height within the cavity (H 0/R 0 ~ 0.6). An ISM dust-to-gas ratio (d:g = 10−2) yields too little line-wing flux, regardless of the scale-height or cavity gas geometry, while a smaller scale-height also under-predicts the flux even with a reduced d:g. (3) The cavity gas mass is consistent with the surface density profile of the outer disk extended inwards to the sublimation radius (corresponding to mass M d ~ 0.03 M ⊙), and masses lower by a factor gsim10 appear to be ruled out.
Pascucci I, Testi L, Herczeg GJ, et al., 2016, A steeper than linear disk mass-stellar mass scaling relation, Astrophysical Journal, Vol: 831, ISSN: 1538-4357
The disk mass is among the most important input parameter for every planet formation model to determine the number and masses of the planets that can form. We present an ALMA 887 μm survey of the disk population around objects from ~2 to 0.03 M ⊙ in the nearby ~2 Myr old Chamaeleon I star-forming region. We detect thermal dust emission from 66 out of 93 disks, spatially resolve 34 of them, and identify two disks with large dust cavities of about 45 au in radius. Assuming isothermal and optically thin emission, we convert the 887 μm flux densities into dust disk masses, hereafter M dust. We find that the ${M}_{\mathrm{dust}}\mbox{--}{M}_{* }$ relation is steeper than linear and of the form M dust ∝ (M *)1.3–1.9, where the range in the power-law index reflects two extremes of the possible relation between the average dust temperature and stellar luminosity. By reanalyzing all millimeter data available for nearby regions in a self-consistent way, we show that the 1–3 Myr old regions of Taurus, Lupus, and Chamaeleon I share the same ${M}_{\mathrm{dust}}\mbox{--}{M}_{* }$ relation, while the 10 Myr old Upper Sco association has a steeper relation. Theoretical models of grain growth, drift, and fragmentation reproduce this trend and suggest that disks are in the fragmentation-limited regime. In this regime millimeter grains will be located closer in around lower-mass stars, a prediction that can be tested with deeper and higher spatial resolution ALMA observations.
Haworth TJ, Ilee JD, Forgan DH, et al., 2016, Grand challenges in protoplanetary disc modelling, Publications of the Astronomical Society of Australia, Vol: 33, ISSN: 1448-6083
The Protoplanetary Discussions conference—held in Edinburgh, UK, from 2016 March 7th–11th—included several open sessions led by participants. This paper reports on the discussions collectively concerned with the multi-physics modelling of protoplanetary discs, including the self-consistent calculation of gas and dust dynamics, radiative transfer, and chemistry. After a short introduction to each of these disciplines in isolation, we identify a series of burning questions and grand challenges associated with their continuing development and integration. We then discuss potential pathways towards solving these challenges, grouped by strategical, technical, and collaborative developments. This paper is not intended to be a review, but rather to motivate and direct future research and collaboration across typically distinct fields based on community-driven input, to encourage further progress in our understanding of circumstellar and protoplanetary discs.
Owen JE, Mohanty S, 2016, Habitability of terrestrial-mass planets in the HZ of M Dwarfs - I. H/He-dominated atmospheres, Monthly Notices of the Royal Astronomical Society, Vol: 459, Pages: 4088-4108, ISSN: 1365-2966
The ubiquity of M dwarfs, combined with the relative ease of detecting terrestrial-mass planets around them, has made them prime targets for finding and characterizing planets in the ‘habitable zone’ (HZ). However, Kepler finds that terrestrial-mass exoplanets are often born with voluminous H/He envelopes, comprising mass-fractions (Menv/Mcore) ≳1 per cent. If these planets retain such envelopes over Gyr time-scales, they will not be ‘habitable’ even within the HZ. Given the strong X-ray/UV fluxes of M dwarfs, we study whether sufficient envelope mass can be photoevaporated away for these planets to become habitable. We improve upon previous work by using hydrodynamic models that account for radiative cooling as well as the transition from hydrodynamic to ballistic escape. Adopting a template active M dwarf XUV spectrum, including stellar evolution, and considering both evaporation and thermal evolution, we show that: (1) the mass-loss is (considerably) lower than previous estimates that use an ‘energy-limited’ formalism and ignore the transition to Jeans escape; (2) at the inner edge of the HZ, planets with core mass ≲ 0.9 M⊕ can lose enough H/He to become habitable if their initial envelope mass-fraction is ∼1 per cent; (3) at the outer edge of the HZ, evaporation cannot remove a ∼1 per cent H/He envelope even from cores down to 0.8 M⊕. Thus, if planets form with bulky H/He envelopes, only those with low-mass cores may eventually be habitable. Cores ≳1 M⊕, with ≳1 per cent natal H/He envelopes, will not be habitable in the HZ of M dwarfs.
Rodriguez DR, van der Plas G, Kastner JH, et al., 2016, A Molecular Disk Survey of Low-Mass Stars in the TW Hya Association, 314th Symposium of the International-Astronomical-Union (IAU), Publisher: CAMBRIDGE UNIV PRESS, Pages: 207-208, ISSN: 1743-9213
Rodriguez DR, van der Plas G, Kastner JH, et al., 2015, An ALMA survey for disks orbiting low-mass stars in the TW Hya Association, Astronomy & Astrophysics, Vol: 582, ISSN: 1432-0746
We carried out an ALMA survey of 15 confirmed or candidate low-mass (<0.2 M⊙) members of the TW Hya Association (TWA) with the goal of detecting molecular gas in the form of CO emission, as well as of providing constraints on continuum emission due to cold dust. Our targets have spectral types of M4-L0 and hence represent the extreme low end of the TWA’s mass function. Our ALMA survey has yielded detections of 1.3 mm continuum emission around 4 systems (TWA 30B, 32, 33, and 34), suggesting the presence of cold dust grains. All continuum sources are unresolved. TWA 34 further shows 12CO(2–1) emission whose velocity structure is indicative of Keplerian rotation. Among the sample of known ~7–10 Myr-old star/disk systems, TWA 34, which lies just ~50 pc from Earth, is the lowest mass star thus far identified as harboring cold molecular gas in an orbiting disk.
Rugheimer S, Kaltenegger L, Segura A, et al., 2015, Effect of UV radiation on the spectral fingerprints of earth-like planets orbiting M stars, Astrophysical Journal, Vol: 809, ISSN: 1538-4357
We model the atmospheres and spectra of Earth-like planets orbiting the entire grid of M dwarfs for active and inactive stellar models with Teff = 2300 K to Teff = 3800 K and for six observed MUSCLES M dwarfs with UV radiation data. We set the Earth-like planets at the 1 AU equivalent distance and show spectra from the visible to IR (0.4–20 μm) to compare detectability of features in different wavelength ranges with the James Webb Space Telescope and other future ground- and spaced-based missions to characterize exo-Earths. We focus on the effect of UV activity levels on detectable atmospheric features that indicate habitability on Earth, namely, H2O, O3, CH4, N2O, and CH3Cl. To observe signatures of life—O2/O3 in combination with reducing species like CH4—we find that early and active M dwarfs are the best targets of the M star grid for future telescopes. The O2 spectral feature at 0.76 μm is increasingly difficult to detect in reflected light of later M dwarfs owing to low stellar flux in that wavelength region. N2O, another biosignature detectable in the IR, builds up to observable concentrations in our planetary models around M dwarfs with low UV flux. CH3Cl could become detectable, depending on the depth of the overlapping N2O feature. We present a spectral database of Earth-like planets around cool stars for directly imaged planets as a framework for interpreting future light curves, direct imaging, and secondary eclipse measurements of the atmospheres of terrestrial planets in the habitable zone to design and assess future telescope capabilities.
Tottle J, Mohanty S, 2015, Testing model atmospheres for young very-low-mass stars and brown dwarfs in the infrared: evidence for significantly underestimated dust opacities, Astrophysical Journal, Vol: 805, ISSN: 1538-4357
We test state-of-the-art model atmospheres for young very-low-mass stars and brown dwarfs in the infrared, by comparing the predicted synthetic photometry over 1.2–24 μm to the observed photometry of M-type spectral templates in star-forming regions. We find that (1) in both early and late young M types, the model atmospheres imply effective temperatures (${{T}_{{\rm eff}}}$) several hundred Kelvin lower than predicted by the standard pre-main sequence (PMS) spectral type–${{T}_{{\rm eff}}}$ conversion scale (based on theoretical evolutionary models). It is only in the mid-M types that the two temperature estimates agree. (2) The ${{T}_{{\rm eff}}}$ discrepancy in the early M types (corresponding to stellar masses $\gtrsim 0.4$ ${{M}_{\odot }}$ at ages of a few Myr) probably arises from remaining uncertainties in the treatment of atmospheric convection within the atmospheric models, whereas in the late M types it is likely due to an underestimation of dust opacity. (3) The empirical and model-atmosphere J-band bolometric corrections are both roughly flat, and similar to each other, over the M-type ${{T}_{{\rm eff}}}$ range. Thus the model atmospheres yield reasonably accurate bolometric luminosities (${{L}_{{\rm bol}}}$), but lead to underestimations of mass and age relative to evolutionary expectations (especially in the late M types) due to lower ${{T}_{{\rm eff}}}$. We demonstrate this for a large sample of young Cha I and Taurus sources. (4) The trends in the atmospheric model J−Ks colors, and their deviations from the data, are similar at PMS and main sequence ages, suggesting that the model dust opacity errors we postulate here for young ages also apply at field ages.
Yang H, Apai D, Marley MS, et al., 2015, <i>HST</i> ROTATIONAL SPECTRAL MAPPING OF TWO L-TYPE BROWN DWARFS: VARIABILITY IN AND OUT OF WATER BANDS INDICATES HIGH-ALTITUDE HAZE LAYERS, ASTROPHYSICAL JOURNAL LETTERS, Vol: 798, ISSN: 2041-8205
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- Citations: 42
Mohanty S, Greaves J, Mortlock D, et al., 2013, Protoplanetary disk masses from stars to brown dwarfs, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 773, ISSN: 0004-637X
We present SCUBA-2 850 μm observations of seven very low mass stars (VLMS) and brown dwarfs (BDs). Three are in Taurus and four in the TW Hydrae Association (TWA), and all are classical T Tauri (cTT) analogs. We detect two of the three Taurus disks (one only marginally), but none of the TWA ones. For standard grains in cTT disks, our 3σ limits correspond to a dust mass of 1.2 M ⊕ in Taurus and a mere 0.2 M ⊕ in the TWA (3-10× deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, ρ Oph, and the TWA to investigate the trends in disk mass and grain growth during the cTT phase. Assuming a gas-to-dust mass ratio of 100:1 and fiducial surface density and temperature profiles guided by current data, we find the following. (1) The minimum disk outer radius required to explain the upper envelope of sub-mm/mm fluxes is ~100 AU for intermediate-mass stars, solar types, and VLMS, and ~20 AU for BDs. (2) While the upper envelope of apparent disk masses increases with M * from BDs to VLMS to solar-type stars, no such increase is observed from solar-type to intermediate-mass stars. We propose this is due to enhanced photoevaporation around intermediate stellar masses. (3) Many of the disks around Taurus and ρ Oph intermediate-mass and solar-type stars evince an opacity index of β ~ 0-1, indicating significant grain growth. Of the only four VLMS/BDs in these regions with multi-wavelength measurements, three are consistent with considerable grain growth, though optically thick disks are not ruled out. (4) For the TWA VLMS (TWA 30A and B), combining our 850 μm fluxes with the known accretion rates and ages suggests substantial grain growth by 10 Myr, comparable to that in the previously studied TWA cTTs Hen 3-600A and TW Hya. The degree of grain growth in the TWA BDs (2M1207A and SSPM1102) remains largely unknown. (5) A Bayesian analysis shows that the apparent disk-to-stellar mass
Mohanty S, Ercolano B, Turner NJ, 2013, DEAD, UNDEAD, AND ZOMBIE ZONES IN PROTOSTELLAR DISKS AS A FUNCTION OF STELLAR MASS, ASTROPHYSICAL JOURNAL, Vol: 764, ISSN: 0004-637X
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Bochanski JJ, Hawley SL, Covey KR, et al., 2013, Measuring the ages of low-mass stars and brown dwarfs, ASTRONOMISCHE NACHRICHTEN, Vol: 334, Pages: 44-47, ISSN: 0004-6337
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Costigan G, Scholz A, Stelzer B, et al., 2012, LAMP: the long-term accretion monitoring programme of T Tauri stars in Chamaeleon I, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 427, Pages: 1344-1362, ISSN: 0035-8711
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- Citations: 59
Mohanty S, Stassun KG, 2012, HIGH-RESOLUTION SPECTROSCOPY DURING ECLIPSE OF THE YOUNG SUBSTELLAR ECLIPSING BINARY 2MASS 0535-0546. II. SECONDARY SPECTRUM: NO EVIDENCE THAT SPOTS CAUSE THE TEMPERATURE REVERSAL, ASTROPHYSICAL JOURNAL, Vol: 758, ISSN: 0004-637X
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- Citations: 6
Reiners A, Mohanty S, 2012, RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I, ASTROPHYSICAL JOURNAL, Vol: 746, ISSN: 0004-637X
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- Citations: 156
Burgasser AJ, Simcoe RA, Bochanski JJ, et al., 2012, Cool Star Science with the FIRE Spectrograph, 16TH CAMBRIDGE WORKSHOP ON COOL STARS, STELLAR SYSTEMS AND THE SUN, Vol: 448, Pages: E573-E580
Pascucci I, Laughlin G, Gaudi BS, et al., 2012, Planet Formation Around M-dwarf Stars: From Young Disks to Planets, 16th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun, Publisher: ASTRONOMICAL SOC PACIFIC, Pages: 469-479
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Dib S, Piau L, Mohanty S, et al., 2011, Star formation efficiency as a function of metallicity: from star clusters to galaxies, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 415, Pages: 3439-3454, ISSN: 0035-8711
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- Citations: 42
Kaltenegger L, Segura A, Mohanty S, 2011, MODEL SPECTRA OF THE FIRST POTENTIALLY HABITABLE SUPER-EARTH-Gl581d, ASTROPHYSICAL JOURNAL, Vol: 733, ISSN: 0004-637X
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- Citations: 44
Pascucci I, Laughlin G, Gaudi BS, et al., 2011, Planet Formation Around M-dwarf Stars: From Young Disks to Planets, 16TH CAMBRIDGE WORKSHOP ON COOL STARS, STELLAR SYSTEMS AND THE SUN, Vol: 448, Pages: 469-+
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