HD An Evolutionary Link Between Protoplanetary Disks and Debris Disks

Journal Paper Co-authors Karen CollinsMaster's Thesis Defense4/24/2008 Co-authors(s)AffiliationContribution C. A. GradyEureka Scientific and NASA GSFCoverall direction, science mentor, HST and Chandra PI, and day-to-day support K. Hamaguchi & R. PetreX-ray Astrophysics Laboratory NASA/GSFC Chandra observations, data reduction, and results J. P. WisniewskiNASA/GSFC, NPP FellowHST ACS HRC observations, data reduction, and results S. BrittainClemson UniversityGemini South observations of warm CO, data reduction, and results M. Sitko & W. J. CarpenterSSI, University of CincinnatiSED and modeling data, general support G. M. WilligerUniversity of LouisvilleFUSE observations, data reduction, results, and general day-to-day support R. van BoekelMax-Planck-Institut für AstronomieVLT NACO NIR observations, data reduction, common proper motion results, and related photometric results A. CarmonaMax-Planck-Institut für Astronomie, ESO, ISDC & Geneva Observatory VLT SINFONI NIR spectroscopy, data reduction, spectral typing, and other related results. M. E. van den AnckerEuropean Southern ObservatoryVLT SINFONI NIR spectroscopy, data reduction, spectral typing, and other related results. G. MeeusAstrophysikalisches Institut PotsdamFEROS Ca II spectroscopic data J. P. Williams, G. S. Mathews University of HawaiiJCMT HARP CO spectroscopic observations, data reduction, dust mass calculations, gas mass calculations, and related results X. P. ChenMax-Planck-Institut für AstronomieVLT NACO Brγ common proper motion data reduction B. E. WoodgateNASA/GSFCoverall scientific interpretation Th. HenningMax-Planck-Institut für Astronomieoverall scientific interpretation

Karen CollinsMaster's Thesis Defense4/24/2008 Star Formation Overview Start with molecular cloud Four phases of collapse dense rotating core forms collapses from inside out bipolar outflows carry away angular momen. (L) star and disk revealed Conservation of L cloud rotates slowly star rotates more rapidly High L material forms disk disk accretes onto star Shu et al Wood 1997

Pre-Main Sequence Stars Pre-main sequence (PMS) stars fully revealed stars still gravitationally contracting toward main sequence hydrogen fusion not started yet PMS stars are called T Tauri if 0.1 M < M < 2 M (M, K, G, F type stars) Herbig Ae/Be if 2 M < M < 8 M (F, A, B type stars) higher mass stars emerge from cloud on main sequence Observable characteristics Balmer emission lines in stellar spectrum (Hα, Hβ, Hγ, …) transition (3 2, 4 2, 5 2, …) infrared excess due to circumstellar dust (next slides) Karen CollinsMaster's Thesis Defense4/24/2008

Spectral Energy Distribution Spectral Energy Distribution (SED) plot of radiated energy vs. wavelength Stellar photosphere ~blackbody peaks in optical Sun 5778 K A-type stars ,000 K M-type stars K

Infrared Excess IR excess total emission stellar contribution stellar contribution determined from a model fit to UV and Optical data source is circumstellar dust dust absorbs stellar radiation re-radiates as thermal emission IR excess source inner disk NIR (1 - 7 μm) outer disk MID to FIR ( μm) disk midplane FIR to mm (>50 μm) Karen CollinsMaster's Thesis Defense4/24/2008 adapted from M.Sitko simulation

Disk Evolution Protoplanetary Disks (initial phase) gas rich + small dust grains (submicron) gas:dust ~100:1 (as in interstellar medium (ISM)) high accretion rates (> ~ M yr 1 ) gas and dust well mixed hydrostatic equilibrium dust material supported above midplane disk can maintain scale height disk expected to flare Karen CollinsMaster's Thesis Defense4/24/2008

Flared Disk "bowl" shaped disk h r, where > 1.0 relatively flat SED in IR inner rim NIR BB disk surface MIR - FIR disk midplane FIR - mm Karen CollinsMaster's Thesis Defense4/24/2008 Dullemond et al. 2006

Disk Vertical Structure inner-most part of the disk is dust free beyond sublimation temperature the inner rim is illuminated face-on from the star, the gas heats up more and causes an increased scale height (i.e. it "puffs up") as the disk ages, the dust grains grow in size disk becomes vertically stratified larger grains in midplane smaller grains in upper layers Karen CollinsMaster's Thesis Defense4/24/2008 Dullemond et al. 2006

Disk Evolution Continued Transitional Disks (intermediate phase) accretion rates ~ x lower than protoplanetary disks IR excess similar to pp disk at >10 μm IR excess significantly less at <10 μm result of less dust, or optically thin dust, in the inner disk photoevaporation grain growth until optically thin gap creation by massive planet Karen CollinsMaster's Thesis Defense4/24/2008

Disk Evolution Continued Debris Disks (final phase) accretion has stopped moderate IR excess at >10 μm very little to no IR excess at <10 μm no inner disk at all primordial dust has grown to rocks, protoplanets, and terrestrial planets remaining dust is second generation from collisions of massive bodies gas-poor Karen CollinsMaster's Thesis Defense4/24/2008 Van den Ancker 1999

Meeus Groups Meeus et al. (2001) divided 14 Herbig stars into two groups Group I blackbody in MIR high fraction of IR excess (L IR /L * ~ 0.5) steep submm slope (i.e. small grains) Group II no blackbody in MIR low fraction of IR excess (L IR /L * ~ 0.2) shallow submm slope (i.e. larger grains) Meeus et al. suggested Group I sources evolve to Group II sources Karen CollinsMaster's Thesis Defense4/24/2008

Meeus Physical Model 3 components disk midplane - optically thick inner disk with scale height outer disk Group I inner disk optically thin outer disk is directly illuminated outer disk heats & flares creates MIR BB Group II inner disk optically thick outer disk shielded outer disk stays flat no MIR BB Karen CollinsMaster's Thesis Defense4/24/2008

Thesis Goal Test idea that Meeus Group I sources evolve to Meeus Group II sources at time of Meeus et al. (2001) paper, many age estimates were not available accretion rates were not considered (recall that accretion rate is tied to disk evolution) Karen CollinsMaster's Thesis Defense4/24/2008

Thesis Approach Compare ages and accretion rates between the groups we focus on HD in this work because: Herbig AeBe stars are difficult to date after about 5 Myr low-mass stars are easier to date and often form together with A-stars we can determine the age of the A-star from a companion low-mass star a candidate low-mass companion was recently reported for HD A (Chen et al. 2006) determine age and accretion rate for HD A (this work) determine age and accretion rate for other stars from the literature Karen CollinsMaster's Thesis Defense4/24/2008

HD A Karen CollinsMaster's Thesis Defense4/24/2008 Southern Hemisphere (Lower Centaurus-Crux Assn) Distance 114 pc v=7.78 (not visible by naked eye) Spectral Type A9Ve Age > ~10 Myr

Summary of Observations Karen CollinsMaster's Thesis Defense4/24/2008 InstrumentPrimeDirect Image Coron. Image SpectraWavelengthScientific Purpose ChandraK. Hamaguchi X-rayAccretion Rate HST ACS HRCJ. Wisniewski OpticalCompanion Location & Photometry HST ACS HRCJ. Wisniewski OpticalDisk Detection & Photometry HST ACS SBCC. Grady K. Collins FUVCompanion Detection VLT NACOR van Boekel NIRCompanion Proper Motion & Photometry VLT SINFONIA. Carmona NIRSpectral Type of Companion FUSEG.M. Williger FUVAccretion Rate PhoenixS. Brittain NIRWarm Gas Limits JCMT HARPJ. Williams G. Mathews SubmmCold Gas Limits FEROSG. Meeus K. Collins OpticalAccretion Rate

Test of Companion Status To date an A-star from a low-mass companion, we need to know that they are physical companions Two tests: determine motion of A-star & candidate companion If motion through space is common, they are likely physical companions determine spectral type of companion for the brightness contrast between the two stars, a physical companion would be a low-mass star Karen CollinsMaster's Thesis Defense4/24/2008

The Candidate Companion HST optical direct image B located 126° east of north m v = (A:B = 1500:1 contrast) Karen CollinsMaster's Thesis Defense4/24/2008 optical HST ACS HRC F606W

Candidate Companion Spectral Type Need high spatial resolution spectroscopy to separate the light from the two stars Optical Spectroscopy is first choice need A/O for ~1 separation none available NIR is good second choice SINFONI on VLT with A/O Integral Field Spectrograph 0.8 x 0.8 field of view J, H, K band gratings (NIR) Karen CollinsMaster's Thesis Defense4/24/2008

Candidate Companion Spectral Type Karen CollinsMaster's Thesis Defense4/24/2008

Relative Proper Motion Karen CollinsMaster's Thesis Defense4/24/2008

Candidate Confirmation Karen CollinsMaster's Thesis Defense4/24/2008

Companion Photometry ObjectModeFiltermagnitudeNotes (prime) HD BDirectm F606W 15.6HST HRC (J. Wisniewski) HD BCoronm F606W 15.8HST HRC (J. Wisniewski) HD BCombinedm F606W (J. Wisniewski) HD BDirectKsKs (Chen et al. 2006) HD BCoron L VLT NACO (R. van Boekel) HD BCoron M VLT NACO (R. van Boekel) HD BCalculatedV (K. Collins) HD BCalculatedK (K. Collins) HD BCalculatedL (K. Collins) Karen CollinsMaster's Thesis Defense4/24/2008 Key Point: Candidate companion has NO IR Excess Can use K-band in H-R diagram for age estimate

Age Determination (from A-star) Karen CollinsMaster's Thesis Defense4/24/2008

Age Determination (from Companion) Note wider separation of isochrones for low-mass stars HD B (input data) m K = ± 0.1 M4.0V – M4.5V T eff = 3300 K – 3400 K Results (Siess Model) age: Myr mass: M Results (Baraffe Model) age: Myr mass: M Results (Combined) age: 14 ± 4 Myr mass: M Karen CollinsMaster's Thesis Defense4/24/2008

Mass Accretion onto A-star Mass accretion rate gives insight into the evolutionary phase of the disk We investigate the following accretion indicators: enhanced FUV continuum Herbig-Haro knots in Lyα enhanced emission of Ca II λ8662 Å Hard X-rays Hα (6563 Å) Brγ (2.166 μm) Karen CollinsMaster's Thesis Defense4/24/2008

Accretion - FUV Continuum FUV continuum upper limit from FUSE spectra < ergs s 1 cm 2 Å 1 (1σ) (-14.8 in log space) Karen CollinsMaster's Thesis Defense4/24/2008

Accretion - FUV Continuum Karen CollinsMaster's Thesis Defense4/24/2008 Plot accretion rate vs. FUV continuum accretion rates based on Brγ (Garcia Lopez et al. 2006) FUV values from literature note power law trend except HD

Accretion - FUV Continuum Karen CollinsMaster's Thesis Defense4/24/2008

Accretion - Herbig-Haro Knots Karen CollinsMaster's Thesis Defense4/24/2008 HST ACS SBC F122M FUV

Accretion- Ca II 8662 Å emission Karen CollinsMaster's Thesis Defense4/24/2008

Accretion - Hα Karen CollinsMaster's Thesis Defense4/24/2008

Accretion - X-ray Karen CollinsMaster's Thesis Defense4/24/2008 Chandra red keV green keV blue keV energy (keV) 1 2 Chandra X-ray HD A HD B

Accretion Rate Summary Accretion IndicatorAccretion LevelSignificance FUV Continuum< 2.5×10 10 M yr 1 1 Lack of Ca II 8662 Å emission line < 1.0×10 10 M yr 1 4 Lack of HH Knots in Ly < ~6×10 11 M yr 1 factor of 10 H weak accretor X-raynot strong accretor Karen CollinsMaster's Thesis Defense4/24/2008

Constraints on Disk Structure Karen CollinsMaster's Thesis Defense4/24/2008 M. Sitko, private communication Habart et al. (2006)

HST ACS Coronagraphy Need ~1x10 6 contrast to image disk around A star Use coronagraph to block light from central star Use psf-subtraction to reduce remaining stray light ACS HRC provides contrast of: ~1x10 5 in direct mode ~1x10 6 in coronagraphic mode ~1x10 7 in coronagraphic mode with psf-subtraction HRC has 0".9 radius spot size, but psf-subtraction residuals out to ~2-3" Karen CollinsMaster's Thesis Defense4/24/2008 Clampin et al. 2003

Constraints on Disk Structure Karen CollinsMaster's Thesis Defense4/24/2008 HST ACS HRC Coron w/psf-sub HD

Constraints on Disk Structure Karen CollinsMaster's Thesis Defense4/24/2008 HST ACS (red) VLT NACO (blue)

Disk Structure Summary Karen CollinsMaster's Thesis Defense4/24/2008 C B A Gap (SED dip)? i ? Inner Rim <0.5 AU (NIR BB) Outer Radius >40 AU (PAH) Outer Edge Optically Thin <90 proj. AU (star C) Companion 120 proj. AU Scattered Light Outer Radius <250 AU Line of Sight

Gas and Dust in Inner Disk Karen CollinsMaster's Thesis Defense4/24/2008 (after Brittain et al. 2007)

Gas and Dust in Outer Disk Karen CollinsMaster's Thesis Defense4/24/2008

Where Does It Belong? 14 ± 4 Myr transitional disk character High NIR excess protoplanetary disk character Low accretion rate transitional or debris disk character Gas-poor disk debris disk character High total IR excess flared disk? requires gas? HD A does not fit in any classically defined disk group (protoplanetary, transitional, debris) Karen CollinsMaster's Thesis Defense4/24/2008

Thesis Results Karen CollinsMaster's Thesis Defense4/24/2008 Recall we set out to test idea that Meeus Group I sources evolve to Group II... by comparing ages & accretion between the groups determine for HD collect new and updated data from literature

Thesis Results Karen CollinsMaster's Thesis Defense4/24/2008 Group I sources are slightly older than Group II on average (but are within 1σ) Group I accretion rates are slightly lower than Group II accretion rates on average (but are within 1σ)

Thesis Results Age range significantly overlaps between the two groups Accretion slows as star ages in both groups Meeus suggested star and disk evolution may be decoupled for this sample We find that the star, accretion rate, and disk evolve together. We conclude that the hypothesis suggesting Meeus Group I sources evolve to Meeus Group II sources does not hold. Karen CollinsMaster's Thesis Defense4/24/2008

Possible Physical Explanation HD example (Group I) cavity confirmed by interferometry & STIS (Lui et al. 2003) (Grady et al. 2005) inner rim of inner and outer disk creates NIR and MIR blackbody components in SED and high L excess /L * possible giant planet in gap is causing collisional cascade collisions produce small dust grains radiation pressure blows the grains onto surface of cold outer disk small grains cause steep submm slope Meeus groups may be more representative of differences in disk structure rather than differences in disk evolution. Karen CollinsMaster's Thesis Defense4/24/2008 after Bouwman et al. 2003)

Future Directions To lift disk structure degeneracy allowed by SED need high contrast, high spatial resolution imaging high spatial resolution interferometry We can do this with existing instrumentation NICMOS on HST ( coron. imaging, pixel 1, 0".3 hole) My collaborators have submitted a proposal (March 2008) for NICMOS observations of several T Tauri and Herbig Ae/Be stars, including HD Near-term prospects HST SM4 (8/2008) set to repair other key instruments ACS (down since June 2006) coron. imaging mode, pixel 1, 0".9 radius spot STIS (down since 2004) coron. imaging mode, 0.05 pixel 1, 0".5-2.8" wedges Karen CollinsMaster's Thesis Defense4/24/2008 HD (from Krist 2004)

Long -Term Prospects Atacama Large Millimeter Array (ALMA) mm (cold dust and gas) 0".01 resolution, no occulter needed 64 x 12-meter antennas completion expected in 2012 Simulation 0.5 M star 1 M J planet 5 AU orbit M disk = 10 M J Karen CollinsMaster's Thesis Defense4/24/2008 Wolf & D'Angelo 2005

Karen CollinsMaster's Thesis Defense4/24/2008 A possible view of the HD system? adapted from NASA/JPL-Caltech/T. Pyle (SSC) Thank You!