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Mass accretion in the Trapezium Cluster Massimo Robberto (ESA-STScI)

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Presentation on theme: "Mass accretion in the Trapezium Cluster Massimo Robberto (ESA-STScI)"— Presentation transcript:

1 Mass accretion in the Trapezium Cluster Massimo Robberto (ESA-STScI)

2 Feb. 16, 2004STScI Star/ISM Journal Club Star formation: the standard paradigm Cloud collapse 10 4 yr Disk/wind 10 5 yr Planetary system 10 9 yr10 7 yr Low-mass binary

3 Feb. 16, 2004STScI Star/ISM Journal Club Star formation: the current paradigm Cloud collapse 10 4 yr Disk/wind 10 5 yr Planetary system 10 9 yr10 7 yr Low-mass binary

4 Feb. 16, 2004STScI Star/ISM Journal Club The current paradigm: data

5 Feb. 16, 2004STScI Star/ISM Journal Club Disk accretion Regulates the final stellar mass Regulates the final stellar mass Removes angular momentum Removes angular momentum Feeds collimated mass outflow Feeds collimated mass outflow Disk accretion is responsible for Disk accretion is responsible for - IR emission of “active” disks - Hot (UVis) continuum at the stellar surface Uvis radiation Uvis radiation - affects disk chemistry - contributes to disk dissipation

6 Feb. 16, 2004STScI Star/ISM Journal Club IR disk emission L*L* r  Power/area absorbed ~ L * 4  r 2 sin   L * 4  r 2 rr ~ L * r 3 ~ Power/area emitted =  T 4 L * r 3 ~ (r >>  ) T(r) ~ r -3/4 Star of luminosity, L *, surrounded by thin, flat, black disk. 1. Passive 2. Active r r+  r Potential energy released by inflowing accreting material

7 Feb. 16, 2004STScI Star/ISM Journal Club UVis spectrum of T Tauri stars Gullbring et al. (1998 )

8 Feb. 16, 2004STScI Star/ISM Journal Club Accretion spectrum Gullbring et al. (1998 )

9 Feb. 16, 2004STScI Star/ISM Journal Club Magnetospheric model (Königl 1991, Camenzind 1990)

10 Feb. 16, 2004STScI Star/ISM Journal Club Support for magnetospheric model 1. hot spots rotating with the star (because of its magnetic field structure) 2. absence of inner disk emission in some stars (Bertout et al. 1988) 3. slower rotation of stars with inner disks (Bouvier et al. 1993; Edwards et al. 1993), which can be explained by the disk torques communicated to the star by the magnetic field (Königl 1991; Shu et al. 1994) 4. the emission profiles of permitted lines, in particular inverse P Cygni redshifted absorption features (Edwards et al. 1994), which can be accounted for by emitting gas in free fall along the magnetosphere (Hartmann, Hewett, & Calvet 1994)

11 Feb. 16, 2004STScI Star/ISM Journal Club Accretion shock models Gullbring et al. ApJ 544, 927 (2000)

12 Feb. 16, 2004STScI Star/ISM Journal Club Measuring the accretion: Veiling 10 2 reference accretion 12 4 veiled star

13 Feb. 16, 2004STScI Star/ISM Journal Club Mass accretion evolves with time Hartmann et al. (1998 )

14 Feb. 16, 2004STScI Star/ISM Journal Club Measuring the accretion: UV excess Gullbring et al. (1998 )

15 Feb. 16, 2004STScI Star/ISM Journal Club Accretion luminosity -> mass accretion rate from T eff and from T eff and from the models from the models L acc from the UV excess L acc from the UV excess R d = 3…5 from the models R d = 3…5 from the models

16 Feb. 16, 2004STScI Star/ISM Journal Club The Orion Nebula Cluster (ONC) (a) WFI+ESO/MPIA 2.2m 8k×8k mosaic. U J -band, 5×300s (Dec.2002, mr) (b) 2mass JHK color composite 10 arcmin 1 pc

17 Feb. 16, 2004STScI Star/ISM Journal Club ONC facts Rich: approximately 3500 stars identified within 2.5  2.5pc Dense: ~700 stars in the inner 0.6x0.6pc (n~50,000 pc -3 ) Young (  ~1Myr), rich aggregate of pre-main- sequence (PMS) stars Masses range from 45M  to less than ~0.02 M  Low extinction: at least ~50% of the stars are detected in the visible from the ground L. Hillenbrand 1997, AJ116, 1816

18 Feb. 16, 2004STScI Star/ISM Journal Club The Trapezium Cluster (a) WFI+ESO/MPIA 2.2m 8k×8k mosaic. U J -band, 5×300s (Dec.2002, mr) (b) 2mass JHK color composite 10 arcmin 1 pc

19 Feb. 16, 2004STScI Star/ISM Journal Club The Trapezium Cluster HST/WFPC2 Ha+[OIII]+[SII] (Courtesy C.R.O’Dell)

20 Feb. 16, 2004STScI Star/ISM Journal Club HST data: proplyds 400 AU 2000 AU Section of the Orion Nebula O’Dell & Wen 1992, Ap.J., 387, 229; McCaughrean & O’Dell 1996, AJ, 108, 1382.

21 Feb. 16, 2004STScI Star/ISM Journal Club The ONC stellar populations: recent studies Hillenbrand, AJ 113, 1733 (1997) Hillenbrand, AJ 113, 1733 (1997)  database of 983 spectral types with Hydra/RCSP at Kitt Peak  V-I c photometry for ~1500 stars,  m=0.2mag. Hillenbrand et al., AJ 116, 1816 (1998) Hillenbrand et al., AJ 116, 1816 (1998)  JHK photometry for ~1500 stars Hillenbrand & Carpenter, ApJ 540, 236 (2000) Hillenbrand & Carpenter, ApJ 540, 236 (2000)  Keck HK photometry for 778 stars Rebull et al., AJ 119, 3026 (2000) Rebull et al., AJ 119, 3026 (2000)  V-Ic photometry for ~5000 stars, U photometry for 1600  Flanking fields only Luhman et al., Ap.J. 540, 1016 (2000) Luhman et al., Ap.J. 540, 1016 (2000)  NICMOS/HST JHK photometry Lucas & Roche, MNRAS 314, 858 (2000) Lucas & Roche, MNRAS 314, 858 (2000)  UKIRT JHK photometry Muench et al. ApJ 573, 366 (2002) Muench et al. ApJ 573, 366 (2002)  NTT JHKL photometry

22 Feb. 16, 2004STScI Star/ISM Journal Club Hillenbrand 1997 spectral types for ~1000 stars V, I phtometry down to [I]~18 m and [V]~21 for ~1500 stars. The survey is complete to 1.0M  and samples masses at the H-burning limit (M H ~0.075M  )

23 Feb. 16, 2004STScI Star/ISM Journal Club A pre-main sequnce galore Hillenbrand A v from V-I and T eff 2.BC from T eff 3.L * from V, A v, BC 4.R * from L *,T eff 5.M * and age from L *,T eff, models But mass accretion rates still missing

24 Feb. 16, 2004STScI Star/ISM Journal Club The initial mass function Hillenbrand & Carpenter 2000

25 Feb. 16, 2004STScI Star/ISM Journal Club HST/WFPC2 survey in U and B bands 6 WFPC2 orbits in March WFPC2 orbits in March fields imaged in F336W and F439W 4 fields imaged in F336W and F439W F336W exposures: F336W exposures:  1 s  30 s  4×400 s F439W exposures: F439W exposures:  1 s  30 s  2×180 s

26 Feb. 16, 2004STScI Star/ISM Journal Club The 4 fields Field1 F439W, 180 s Field3 F336W, 300 s Field2 F336W, 300 s Field4 F336W, 180 s North

27 Feb. 16, 2004STScI Star/ISM Journal Club Data reduction HST data pipeline delivers data corrected for HST data pipeline delivers data corrected for  Bias  Dark current  Flat-field Further preparation needed: Further preparation needed:  Bad columns  Hot pixels  Cosmic rays Use A. Dolphin’s HSTPHOT package Use A. Dolphin’s HSTPHOT package  WFPC2 Stellar Photometry with HSTphot, A. E. Dolphin 2000, PASP, 112, 1383 

28 Feb. 16, 2004STScI Star/ISM Journal Club Sources we neglect…

29 Feb. 16, 2004STScI Star/ISM Journal Club …sources we accept Single, isolated, well subtracted (possibly) point sources DataHSTphotresiduals

30 Feb. 16, 2004STScI Star/ISM Journal Club UV database of point sources 91 Sources with F336W photometry 91 Sources with F336W photometry 71 Sources with F439W photometry 71 Sources with F439W photometry 49 Sources with both F336W and F439W 49 Sources with both F336W and F439W 41 with spectral classification from H97 41 with spectral classification from H97 Spectral types in the range Spectral types in the range from G8-K1 to M5.5

31 Feb. 16, 2004STScI Star/ISM Journal Club Analysis 1. Assume a set of template spectra 2. For each template, calculate the F439W, F547M, and F791W (or BVI) magnitudes for different amounts of extinction 3. Fit to the observed BVI colors to find the extinction 4. Correct V and find the bolometric luminosity 5. Find expected, reddened fluxes at other wavelengths and compare with observations

32 Feb. 16, 2004STScI Star/ISM Journal Club 1. Template Spectra Bruzual-Persson-Gun-Stryker Spectral Atlas An extension of the Gunn-Stryker (1983) optical atlas to the UV and near-IR An extension of the Gunn-Stryker (1983) optical atlas to the UV and near-IR Contains several dwarfs belonging to Praesepe and Hyades, representative of PMS population Contains several dwarfs belonging to Praesepe and Hyades, representative of PMS population T eff vs. V-I c relation of H97 T eff vs. V-I c relation of H97

33 Feb. 16, 2004STScI Star/ISM Journal Club 2. Calculate magnitudes of reddened templates 1. Use Synphot 2. Which reddening law? Orion is “anomalous” Higher R v means that higher A v is needed to produce the same E(B-V); grayer dust (larger grains). It increases the estimated stellar luminosity

34 Feb. 16, 2004STScI Star/ISM Journal Club F336W reddening

35 Feb. 16, 2004STScI Star/ISM Journal Club Red-leak in the F336W filter response Red – leak must be taken into account and corrected F336W is entirely below the Balmer discontinuity

36 Feb. 16, 2004STScI Star/ISM Journal Club Use Synphot: the HST photometry simulator Synphot probed to be better than 0.1% on the latest Sp.Types (but with Av=0) red leak %

37 Feb. 16, 2004STScI Star/ISM Journal Club 3. SED fit Gullbring et al. ApJ 544, 927 (2000) The observed flux is a combination of stellar and accretion continua. Accretion continuum modeled as a plane parallel slab of high density gas using Cloudy. Use iterative process to calculate A v and U acc

38 Feb. 16, 2004STScI Star/ISM Journal Club Problem with H97 data: A v =0 for 1/5 of the stars Cause: old HST/WFC photometry shows ~0.4 m scatter vs. WFPC2 data Solution: download and reduce 51 fields (~200 images) of WFPC2 data in F547M and F791W data quality (1991 pre-costar data) data reduction (1993 pipeline) variability

39 Feb. 16, 2004STScI Star/ISM Journal Club Variability!

40 Feb. 16, 2004STScI Star/ISM Journal Club 4. Bolometric correction and luminosity Note: colors, effective temperatures and bolometric corrections must be coherent

41 Feb. 16, 2004STScI Star/ISM Journal Club Results R v =3.1 Fits to the SEDs show No negative residuals in U UV excess generally present F547M variability

42 Feb. 16, 2004STScI Star/ISM Journal Club HR diagram

43 Feb. 16, 2004STScI Star/ISM Journal Club Cluster age: ~1Myr

44 Feb. 16, 2004STScI Star/ISM Journal Club IR excess vs. UV excess

45 Feb. 16, 2004STScI Star/ISM Journal Club Mass accretion rates Calculate F336W band excess using dereddened data Calculate F336W band excess using dereddened data Apply Gullbring relation calibrated to our photometric system to get L acc Apply Gullbring relation calibrated to our photometric system to get L acc  Run a large set (~100) of Cloudy models  Select those who match Gullbring in U J  Run in Synphot to calculate U F336W Estimate the mass accretion rate Estimate the mass accretion rate

46 Feb. 16, 2004STScI Star/ISM Journal Club Accretion is present!

47 Feb. 16, 2004STScI Star/ISM Journal Club Source position vs. Trapezium stars

48 Feb. 16, 2004STScI Star/ISM Journal Club Mass accretion rates in the HR diagram

49 Feb. 16, 2004STScI Star/ISM Journal Club Disk evolution Some evidence of mass accretion rate decreasing with time Mass accretion rates are lower than in Taurus

50 Feb. 16, 2004STScI Star/ISM Journal Club Hartmann (1998) – Similarity solution of evolving, expanding disks Fiducial model The mass accretion rate: decreases with time is proportional to the disk mass

51 Feb. 16, 2004STScI Star/ISM Journal Club Final considerations Evolutionary tracks depend on mass accretion… Evolutionary tracks depend on mass accretion… … but we do not see a (obvious) trend Tout, Livio & Bonnel (1999 )

52 Feb. 16, 2004STScI Star/ISM Journal Club Final considerations PMS models (with M  /yr birthline) look OK in OMC PMS models (with M  /yr birthline) look OK in OMC … but why we never observe such a high accretion rate? a) are data inaccurate? b) are models inaccurate? c) …or is there a physical explanation? Palla & Stahler (1999 )

53 Feb. 16, 2004STScI Star/ISM Journal Club Star formation in OB clusters Drop of mass accretion on all stars could be triggered by an external agent Drop of mass accretion on all stars could be triggered by an external agent Obvious candidate: the onset of UV radiation from Obvious candidate: the onset of UV radiation from  1 Ori-C Consequence: low-mass stars do not evolve to their final mass originally set by collapse/fragmentation: “accretion dwarfed” Consequence: low-mass stars do not evolve to their final mass originally set by collapse/fragmentation: “accretion dwarfed” Test: overabundance of low mass stars Test: overabundance of low mass stars

54 Feb. 16, 2004STScI Star/ISM Journal Club The initial mass function Hillenbrand & Carpenter 2000

55 Feb. 16, 2004STScI Star/ISM Journal Club ONC/Taurus brown dwarfs ratio is 12/1 “Relative to the […] IMF for the Trapezium Cluster, the IMF for Taurus exhibits a modest deficit of stars above 1 solar mass (i.e. Steeper slope), the same turnover mass (~0.8 M  ), and a significant Deficit of brown dwarfs”

56 Feb. 16, 2004STScI Star/ISM Journal Club Does the IMF at the low-mass end depend on the presence of OB stars? To provide an answer we need: Deeper U-band photometry Deeper U-band photometry Simultaneous photometry U->K Simultaneous photometry U->K Accurate spectral classification Accurate spectral classification Reliable templates Reliable templates Bolometric correction Bolometric correction Understand the reddening law Understand the reddening law Move further out in the cluster Move further out in the cluster

57 Feb. 16, 2004STScI Star/ISM Journal Club Further studies Sky & Telescope, submitted

58 Feb. 16, 2004STScI Star/ISM Journal Club The Great Orion Nebula

59 Feb. 16, 2004STScI Star/ISM Journal Club UV excess is a powerful method but watch for… Photometric errors Photometric errors Errors in the color calibrations Errors in the color calibrations Errors in spectral typing Errors in spectral typing Errors in the bolometric correction Errors in the bolometric correction Gravity effects that result in different colors than main-sequence stars Gravity effects that result in different colors than main-sequence stars Anomalous extinction Anomalous extinction Binary companions Binary companions Spots Spots …

60 Feb. 16, 2004STScI Star/ISM Journal Club Excess luminosity vs. distance from  1 Ori-C

61 Feb. 16, 2004STScI Star/ISM Journal Club For a star on the Hayashi track, fully convective and evolving at T=const, it is From our measure Thus The accretion luminosity drops more rapidly than the stellar luminosity.

62 Feb. 16, 2004STScI Star/ISM Journal Club The Orion Nebula NGC 1976 At D = 450 pc from the Sun, is the closest site of active high-mass star formation At D = 450 pc from the Sun, is the closest site of active high-mass star formation Is high (b = -19) on the Galactic Plan, and distant Is high (b = -19) on the Galactic Plan, and distant (h = 150 pc) from the plane In an anti-center quadrant (l = 209) In an anti-center quadrant (l = 209) Foreground contamination is low Foreground contamination is low In front of the nearest GMC (OMC-1) In front of the nearest GMC (OMC-1) Background contamination is low Background contamination is low Foreground extinction is low (Av~1.5) Foreground extinction is low (Av~1.5) NOAO

63 Feb. 16, 2004STScI Star/ISM Journal Club Extant HST data on OMC cluster “HST photometry of the Trapezium Cluster”, Prosser et al, ApJ 421, 1994 “HST photometry of the Trapezium Cluster”, Prosser et al, ApJ 421, 1994  PC F547M + F875M photometry of 11 fields  319 stars on ~12 arcmin 2 fields; 33 binaries  Standard reference but 1991 (pre-COSTAR) data  poor spatial resolution  low photometric quality HST#5469 (cycle 4): “Externally illuminated proto-stellar disks and naked Jets” (PI Bally) HST#5469 (cycle 4): “Externally illuminated proto-stellar disks and naked Jets” (PI Bally)  WFPC2 F547M+ recombination lines of 4 fields  Photometry unpublished, currently under reduction by by M.Robberto and J. Song  Short exposures: 3  F547M HST#6666 (cycle 6): “The Mass Function and Binary Star Fraction of the Trapezium Cluster” (PI Stauffer) HST#6666 (cycle 6): “The Mass Function and Binary Star Fraction of the Trapezium Cluster” (PI Stauffer)  WFPC2 F547M + F79W of 14 fields  Repeat of 1991 run, deeper that HST#5467  Photometry unpublished, no paper listed for this proposal ID in the database. Just reduced by us. HST#8894 (cycle 9): “Accretion disks in the Orion Nebula” (PI Beckwith) HST#8894 (cycle 9): “Accretion disks in the Orion Nebula” (PI Beckwith)  WFPC2 F336W(U) + F439W(B) of 4 fields  First UB band observations of the inner core.

64 Frank Modell ©1987 The New Yorker Are we alone? What do you think? "I'll tell you something else I think. I think there are other bowls somewhere out there with intelligent life just like ours.”

65 Feb. 16, 2004STScI Star/ISM Journal Club DAOphot –> DOphot -> HSTphot HSTphot is specifically designed for use with HST WFPC2 data HSTphot is specifically designed for use with HST WFPC2 data HSTphot uses a library of Tiny Tim PSFs for different locations of the star on the camera, as well as locations of the star's center within the pixel HSTphot uses a library of Tiny Tim PSFs for different locations of the star on the camera, as well as locations of the star's center within the pixel It is optimized for running in undersampled conditions It is optimized for running in undersampled conditions It’s easy to use! It’s easy to use!


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