# DrSubhanjoyMohanty

Faculty of Natural SciencesDepartment of Physics

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### Contact

+44 (0)20 7594 7553s.mohanty

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### Location

1010 BlackettBlackett LaboratorySouth Kensington Campus

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## Publications

Publication Type
Year
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69 results found

Mohanty S, Jankovic MR, Tan JC, Owen JEet al., Inside-Out Planet Formation. V. Structure of the Inner Disk as Implied by the MRI, Astrophysical Journal, 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.

Journal article

Hu X, Tan JC, Zhu Z, Chatterjee S, Birnstiel T, Youdin AN, Mohanty Set 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.

Journal article

Haworth TJ, Facchini S, Clarke CJ, Mohanty Set 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).

Journal article

Haworth TJ, Booth RA, Homan W, Decin L, Clarke CJ, Mohanty Set 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.

Journal article

Mulders GD, Pascucci I, Manara CF, Testi L, Herczeg GJ, Henning T, Mohanty S, Lodato Get 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

Journal article

Manara CF, Testi L, Herczeg GJ, Pascucci I, Alcala JM, Natta A, Antoniucci S, Fedele D, Mulders GD, Henning T, Mohanty S, Prusti T, Rigliaco Eet 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.

Journal article

Long F, Herczeg GJ, Pascucci I, Drabek-Maunder E, Mohanty S, Testi L, Apai D, Hendler N, Henning T, Manara CF, Mulders GDet 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.

Journal article

Ricci L, Cazzoletti P, Czekala I, Andrews SM, Wilner D, Szucs L, Lodato G, Testi L, Pascucci I, Mohanty S, Apai D, Carpenter JM, Bowler BPet 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.

Journal article

Drabek-Maunder E, Mohanty S, Greaves J, Kamp I, Meijerink R, Spaans M, Thi W-F, Woitke Pet 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.

Journal article

Pascucci I, Testi L, Herczeg GJ, Long F, Manara CF, Hendler N, Mulders GD, Krijt S, Ciesla F, Henning T, Mohanty S, Drabek-Maunder E, Apai D, Szucs L, Sacco G, Olofsson Jet 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.

Journal article

Haworth TJ, Ilee JD, Forgan DH, Facchini S, Price DJ, Boneberg DM, Booth RA, Clarke CJ, Gonzalez J-F, Hutchison MA, Kamp I, Laibe G, Lyra W, Meru F, Mohanty S, Panic O, Rice K, Suzuki T, Teague R, Walsh C, Woitke Pet 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.

Journal article

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.

Journal article

Rodriguez DR, van der Plas G, Kastner JH, Schneider AC, Faherty JK, Mardones D, Mohanty S, Principe Det 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.

Journal article

Rugheimer S, Kaltenegger L, Segura A, Linsky J, Mohanty Set 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.

Journal article

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.

Journal article

Yang H, Apai D, Marley MS, Saumon D, Morley CV, Buenzli E, Artigau E, Radigan J, Metchev S, Burgasser AJ, Mohanty S, Lowrance PJ, Showman AP, Karalidi T, Flateau D, Heinze ANet al., 2015, HST 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

Journal article

Mohanty S, Greaves J, Mortlock D, Pascucci I, Scholz A, Thompson M, Apai D, Lodato G, Looper Det al., 2013, PROTOPLANETARY DISK MASSES FROM STARS TO BROWN DWARFS, ASTROPHYSICAL JOURNAL, Vol: 773, ISSN: 0004-637X

Journal article

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

Journal article

Bochanski JJ, Hawley SL, Covey KR, Agueeros MA, Baraffe I, Catalan S, Mohanty S, Rice EL, West AAet al., 2013, Measuring the ages of low-mass stars and brown dwarfs, ASTRONOMISCHE NACHRICHTEN, Vol: 334, Pages: 44-47, ISSN: 0004-6337

Journal article

Costigan G, Scholz A, Stelzer B, Ray T, Vink JS, Mohanty Set 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

Journal article

Reiners A, Mohanty S, 2012, RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I, ASTROPHYSICAL JOURNAL, Vol: 746, ISSN: 0004-637X

Journal article

Burgasser AJ, Simcoe RA, Bochanski JJ, Melis C, McMurtry C, Pipher J, Forrest W, Cushing MC, Looper DL, Mohanty Set 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

Journal article

Pascucci I, Laughlin G, Gaudi BS, Kennedy G, Luhman K, Mohanty S, Birkby J, Ercolano B, Plavchan P, Skemer Aet 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

Conference paper

Dib S, Piau L, Mohanty S, Braine Jet al., 2011, The Dependence of the Galactic Star Formation Laws on Metallicity

We describe results from semi-analytical modelling of star formation inprotocluster clumps of different metallicities. In this model, gravitationallybound cores form uniformly in the clump following a prescribed core formationefficiency per unit time. After a contraction timescale which is equal to a fewtimes their free-fall times, the cores collapse into stars and populate theIMF. Feedback from the newly formed OB stars is taken into account in the formof stellar winds. When the ratio of the effective energy of the winds to thegravitational energy of the system reaches unity, gas is removed from the clumpand core and star formation are quenched. The power of the radiation drivenwinds has a strong dependence on metallicity and it increases with increasingmetallicity. Thus, winds from stars in the high metallicity models lead to arapid evacuation of the gas from the protocluster clump and to a reduced starformation efficiency, as compared to their low metallicity counterparts. Wederive the metallicity dependent star formation efficiency per unit time inthis model as a function of the gas surface density Sigma_g. This is combinedwith the molecular gas fraction in order to derive the dependence of thesurface density of star formation Sigma_SFR on Sigma_g. This feedback regulatedmodel of star formation reproduces very well the observed star formation lawsin galaxies extending from low gas surface densities up to the starburstregime. Furthermore, the results show a dependence of Sigma_SFR on metallicityover the entire range of gas surface densities, and can also explain part ofthe scatter in the observations.

Journal article

Dib S, Piau L, Mohanty S, Braine Jet 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

Journal article

Kaltenegger L, Segura A, Mohanty S, 2011, MODEL SPECTRA OF THE FIRST POTENTIALLY HABITABLE SUPER-EARTH-Gl581d, ASTROPHYSICAL JOURNAL, Vol: 733, ISSN: 0004-637X

Journal article

Dib S, Piau L, Mohanty S, Braine Jet al., 2011, Star formation efficiency as a function of metallicity: from star clusters to galaxies

We explore how the star formation efficiency in a protocluster clump isregulated by metallicity dependent stellar winds from the newly formed massiveOB stars (Mstar >5 Msol). The model describes the co-evolution of the massfunction of gravitationally bound cores and of the IMF in a protocluster clump.Dense cores are generated uniformly in time at different locations in theclump, and contract over lifetimes that are a few times their free fall times.The cores collapse to form stars that power strong stellar winds whosecumulative kinetic energy evacuates the gas from the clump and quenches furthercore and star formation. This sets the final star formation efficiency, SFEf.Models are run with various metallicities in the range Z/Zsol=[0.1,2]. We findthat the SFEf decreases strongly with increasing metallicity.TheSFEf-metallicity relation is well described by a decaying exponential whoseexact parameters depend weakly on the value of the core formation efficiency.We find that there is almost no dependence of the SFEf-metallicity relation onthe clump mass. This is due to the fact that an increase (decrease) in theclump mass leads to an increase (decrease) in the feedback from OB stars whichis opposed by an increase (decrease) in the gravitational potential of theclump. The clump mass-cluster mass relations we find for all of the differentmetallicity cases imply a negligible difference between the exponent of themass function of the protocluster clumps and that of the young clusters massfunction. By normalizing the SFEs to their value for the solar metallicitycase, we compare our results to SFE-metallicity relations derived on galacticscales and find a good agreement. As a by-product of this study, we alsoprovide ready-to-use prescriptions for the power of stellar winds of mainsequence OB stars in the mass range [5,80] Msol in the metallicity range wehave considered

Journal article

Pascucci I, Laughlin G, Gaudi BS, Kennedy G, Luhman K, Mohanty S, Birkby J, Ercolano B, Plavchan P, Skemer Aet 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-+

Journal article

Kaltenegger L, Segura A, Mohanty S, 2011, Super-Earths and life - a fascinating puzzle: Example GJ 581d, 276th Symposium of the International-Astronomical-Union on Astrophysics of Planetary Systems: Formation, Structure, and Dynamical Evolution, Publisher: CAMBRIDGE UNIV PRESS, Pages: 376-+, ISSN: 1743-9213

Conference paper

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