Detection of Strong Millimeter Emission from the Circumstellar Dust Disk Around V1094 Sco: Cold and Massive Disk around a T Tauri Star in a Quiescent Accretion Phase? (original) (raw)
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Large dust particles in disks around T Tauri stars
Astronomy and Astrophysics, 2006
We present 7-mm continuum observations of 14 low-mass pre-main-sequence stars in the Taurus-Auriga star-forming region obtained with the Very Large Array with ∼1. ′′ 5 resolution and ∼0.3 mJy rms sensitivity. For 10 objects, the circumstellar emission has been spatially resolved. The large outer disk radii derived suggest that the emission at this wavelength is mostly optically thin. The millimetre spectral energy distributions are characterised by spectral indices αmm = 2.3 to 3.2. After accounting for contributions from free-free emission and corrections for optical depth, we determine dust opacity indices β in the range 0.5 to 1.6, which suggest that millimetre-sized dust aggregates are present in the circumstellar disks. Four of the sources with β > 1 may be consistent with submicron-sized dust as found in the interstellar medium. Our findings indicate that dust grain growth to millimetre-sized particles is completed within less than 1 Myr for the majority of circumstellar disks.
Strong dust processing in circumstellar discs around 6�RV?Tauri stars
Astronomy and Astrophysics, 2005
We present extended Spectral Energy Distributions (SEDs) of seven classical RV Tauri stars, using newly obtained submillimetre continuum measurements and Geneva optical photometry supplemented with literature data. The broad-band SEDs show a large IR excess with a black-body slope at long wavelengths in six of the seven stars, R Sct being the noticeable exception. This long wavelength slope is best explained assuming the presence of a dust component of large grains in the circumstellar material. We show that the most likely distribution of the circumstellar dust around the six systems is that the dust resides in a disc. Moreover, very small outflow velocities are needed to explain the presence of dust near the sublimation temperature and we speculate that the discs are Keplerian. The structure and evolution of these compact discs are as yet not understood but a likely prerequisite for their formation is that the dusty RV Tauri stars are binaries.
EMISSION FROM DISKS AROUND HERBIG Ae AND T TAURI STARS W.F. Thi
We present the initial results of a deep ISO-SWS survey for the low J pure rotational emission lines of H 2 toward a number of Herbig Ae and T Tauri stars. The objects are selected to be as isolated as possible from molecular clouds, with a spectral energy distribution characteristic of a circumstellar disk. For most of them the presence of a disk has been established directly by millimeter interferometry. The S(1) line is detected in most sources with a peak ux of 0.3{1 Jy. The S(0) line is de nitely seen in 2 objects: GG Tau and HD 163296. The observations suggest the presence of \warm" gas at T kin 100 K with a mass of a few % of the total gas + dust mass, derived assuming a gas-to-dust ratio of 100:1. The S(1) peak ux does not show a strong correlation with spectral type of the central star or continuum ux at 1.3 millimeter. Possible origins for the warm gas seen in H 2 are discussed, and comparisons with model calculations are made.
Continuum and CO/HCO + Emission from the Disk Around the T Tauri Star LkCa 15
The Astrophysical Journal, 2003
We present OVRO Millimeter Array λ = 3.4 − 1.2 mm dust continuum and spectral line observations of the accretion disk encircling the T Tauri star LkCa 15. The 1.2 mm dust continuum emission is resolved, and gives a minimum diameter of 190 AU and an inclination angle of 57 ± 5 • . There is a noticeable, but at present poorly constrained, decrease in the continuum spectral slope with frequency that may result from the coupled processes of grain growth and dust settling. Imaging of the fairly intense emission from the lowest rotational transitions of CO, 13 CO and HCO + reveals a rotating disk substantially larger than that observed in the dust continuum. Emission extends to ∼750 AU and the characteristic radius of the disk is determined to be ∼425 AU (HWHM), based on model fits to the CO velocity field. The measured line ratios demonstrate that the emission from these species is optically thick, while that from C 18 O and H 13 CO + is optically thin, or nearly so. The disk mass derived from the CO isotopologues with "typical" dense cloud abundances is still nearly two orders of magnitude less than that inferred from the dust emission, the most probable explanation being extensive molecular depletion in the cold, dense disk midplane. Thus, while CO, HCO + and their isotopologues are excellent tracers of the disk velocity field, they are not reliable tracers of the disk mass.
Millimeter continuum measurements of circumstellar dust around very young low-mass stars
Astrophysics and Space Science, 1994
C. J. CIIANI)I,IC;IL Chcns Valley Radio obscmaiory 103-24, C'alijornio lnstitutc oj Ykx%nologyf ]'asadcna, CA 91125 1'. ANl)l{fi Service d 'A st roph ysiq UC, Ccntw d'];tudcs dc Saclay, 11'-91I91 G'ij-stir-}'t)cik Ccdcx, ]'h711CC Al] S~'l{AC'J' We illvcstig;atc l,lIc c]ucstio]l of disk for]natio]l during t,lIe ]Jrotostar ]J]Iasc. WC build 011 tlIc results of KcmIIc and hla.sso]l (1990) wlIose analysis of 1,1551 slIowcd tlIc ]nilliInctcr c.o]ltinuuln emission c.oIIIcs fro]]] botlI all u]ircmlvcd c.ircu Instellar com])oIIcmt i.e. disk a]lcl an cxtcIIdwl cloud core, Wc Inoclel the dust c.ontinuu]n cunissio]] from tllc! cloud core a~lcl show it, is i]nport, ant, at 1.3 mm but ncg;ligiblc at 2.7 lnln. Co]nbi]ling IICW 2.7 11~111 OwcI~s Valley lntcrfcro]nctcr data of lRAS-I)CIISC cores with clata from the ]itmaturc wc conc]uclc that massive disks arc also scwII towarcls a ]Iu]nhc.r of ot,hcr sources. ]Iowevcr 1.3 mm data. from the IRAM 3011) tcksc.ope for a larger samp]c shows t}lat massive disks arc relatively rare, occurring arou]ld ]mrhalm 5% of young cIIIhcxldcxl stars. '1'llis i]n])licw that citlicr ]na,ssivc disks occur briefly clurillg the cvnhcxldcd ])hasc or that relatively few you IIg stars form massive disks. At 1,3 ImII tllc ~ncdiall flux of lltAS-l)cmsc corm is nearly tile sa.mc as '1' 'J'auri stars ill tlIc samp]c of IIcckwit]l et al. (1990). We c.ollcludc that I,IIC ty~)ical disk lnass during tlIe cmhldcd pllasc is IIcarly t]lc sa]nc or less t]lall t]lc t,y])ic.a] disk mass during the 'J' 'J'auri phase.
Faint disks around classical T Tauri stars: Small but dense enough to form planets
Astronomy & Astrophysics, 2014
Context. Most Class II sources (of nearby star forming regions) are surrounded by disks with weak millimeter continuum emission. These "faint" disks may hold clues to the disk dissipation mechanism. However, the physical properties of proto-planetary disks have been directly constrained by imaging only the brightest sources. Aims. We attempt to determine the characteristics of such faint disks around classical T Tauri stars, and to explore the link between disk faintness and the proposed disk dispersal mechanisms (accretion, viscous spreading, photo-evaporation, planetary system formation). Methods. We performed high-angular resolution (0.3 ′′) imaging of a small sample of disks (9 sources) with low 1.3 mm continuum flux (mostly < 30 mJy) with the IRAM Plateau de Bure interferometer and simultaneously searched for 13 CO (or CO) J=2-1 line emission. Using a simple parametric disk model, we determine characteristic sizes of the disks, in dust and gas, and we constrain surface densities in the central 50 AU. Results. All disks are much smaller than the bright disks imaged so far, both in continuum and 13 CO lines (5 detections). In continuum, half of the disks are very small, with characteristic radii less than 10 AU, but still have high surface density values. Small sizes appear to be the main cause for the low disk luminosity. Direct evidence for grain growth is found for the three disks that are sufficiently resolved. Low continuum opacity is attested in two systems only, but we cannot firmly distinguish between a low gas surface density and a lower dust emissivity resulting from grain growth. Finally, we report a tentative discovery of a ∼ 20 AU radius cavity in DS Tau, which with the (unresolved) "transition" disk of CX Tau, brings the proportion of "transitional" disks to a similar value to that of brighter sources. The existence of cavities cannot explain by itself their observed low mm flux. Conclusions. This study highlights a category of very compact dust disks, still exhibiting high surface densities, which may represent up to 25% of the whole disk population. While its origin is unclear with the current data alone, it may be related to the compact planetary systems found by the Kepler mission.
Dust Processing in Disks around T Tauri Stars
The Astrophysical Journal, 2006
The 8-14 µm emission spectra of 12 T Tauri stars in the Taurus/Auriga dark clouds and in the TW Hydrae association obtained with the Infrared Spectrograph (IRS 1 ) on board Spitzer are analyzed. Assuming the 10 µm features originate from silicate grains in the optically thin surface layers of T Tauri disks, the 8-14 µm dust emissivity for each object is derived from its Spitzer spectrum. The emissivities are fit with the opacities of laboratory analogs of cosmic dust. The fits include small nonspherical grains of amorphous silicates (pyroxene and olivine), crystalline silicates (forsterite and pyroxene), and quartz, together with large fluffy amorphous silicate grains. A wide range in the fraction of crystalline silicate grains as well as large silicate grains among these stars are found. The dust in the transitional-disk objects CoKu Tau/4, GM Aur, and DM Tau has the simplest form of silicates, with almost no hint of crystalline components and modest amounts of large grains. This indicates that the dust grains in these objects have been modified little from their origin in the interstellar medium. Other
Millimeter-wave Searches for Cold Dust and Molecular Gas around T Tauri Stars in MBM 12
The Astronomical Journal, 2002
We report results of a sensitive search for cold dust and molecular gas in the disks around 8 T Tauri stars in the high-latitude cloud MBM 12. Interferometric observations of 3 mm continuum emission in 5 fields containing 6 of the objects, and literature values for the remaining two, limit the disk masses to M disk < 0.04-0.09 M (gas+dust), for a gas:dust mass ratio of 100 and a distance of 275 pc. By coadding the 3 mm data of our five fields, we set an upper limit to the average disk mass ofM disk (N = 5) < 0.03 M. Simultaneous observation of the CS J=2-1 and the N 2 H + 1-0 lines show no emission. Single-dish observations of the 13 CO 2-1 line limit the disk mass to (5-10)×10 −4 M for a standard CO abundance of 2 × 10 −4. Depletion of CO by up to two orders of magnitude, through freezing out or photodissociation, can reconcile these limits. These mass limits lie within the range found in the Taurus-Auriga and ρ Oph star-forming regions (0.001-0.3 M), and preclude conclusions about possible decrease in disk mass over the 1-2 Myr age range spanned by the latter two regions and MBM 12. Our observations can exclude the presence in MBM 12 of T Tauri stars with relatively bright and massive disks such as T Tau, DG Tau, and GG Tau.
International Astronomical Union Colloquium, 1994
A variety of evidence suggests that at least 50% of T Tauri stars are surrounded by disks of gas and dust. Inferred disk properties are compatible with those generally attributed to the solar nebula, before the formation of planets. Millimeter-wave aperture synthesis mapping of molecular line and dust continuum emission from T Tauri stars provides a direct way to ascertain if disks are present. The technique enables detailed studies of disk temperature and density distributions, chemical properties and velocity fields. These results inform our understanding of both star formation and solar system evolution. We review the observations to date and discuss directions for future research.