Mass accretion in the Trapezium Cluster Massimo Robberto
(ESA-STScI) Slide 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 Slide 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 Slide 4 Feb. 16, 2004STScI
Star/ISM Journal Club The current paradigm: data Slide 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 Slide 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
rr ~ 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 Slide 7 Feb. 16, 2004STScI Star/ISM
Journal Club UVis spectrum of T Tauri stars Gullbring et al. (1998
) Slide 8 Feb. 16, 2004STScI Star/ISM Journal Club Accretion
spectrum Gullbring et al. (1998 ) Slide 9 Feb. 16, 2004STScI
Star/ISM Journal Club Magnetospheric model (Knigl 1991, Camenzind
1990) Slide 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 (Knigl 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) Slide 11 Feb. 16, 2004STScI
Star/ISM Journal Club Accretion shock models Gullbring et al. ApJ
544, 927 (2000) Slide 12 Feb. 16, 2004STScI Star/ISM Journal Club
Measuring the accretion: Veiling 10 2 reference accretion 12 4
veiled star Slide 13 Feb. 16, 2004STScI Star/ISM Journal Club Mass
accretion evolves with time Hartmann et al. (1998 ) Slide 14 Feb.
16, 2004STScI Star/ISM Journal Club Measuring the accretion: UV
excess Gullbring et al. (1998 ) Slide 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 = 35 from the
models R d = 35 from the models Slide 16 Feb. 16, 2004STScI
Star/ISM Journal Club The Orion Nebula Cluster (ONC) (a)
WFI+ESO/MPIA 2.2m 8k8k mosaic. U J -band, 5300s (Dec.2002, mr) (b)
2mass JHK color composite 10 arcmin 1 pc Slide 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 Slide
18 Feb. 16, 2004STScI Star/ISM Journal Club The Trapezium Cluster
(a) WFI+ESO/MPIA 2.2m 8k8k mosaic. U J -band, 5300s (Dec.2002, mr)
(b) 2mass JHK color composite 10 arcmin 1 pc Slide 19 Feb. 16,
2004STScI Star/ISM Journal Club The Trapezium Cluster HST/WFPC2
Ha+[OIII]+[SII] (Courtesy C.R.ODell) Slide 20 Feb. 16, 2004STScI
Star/ISM Journal Club HST data: proplyds 400 AU 2000 AU Section of
the Orion Nebula 114-426 183-405 206-446182-413 ODell & Wen
1992, Ap.J., 387, 229; McCaughrean & ODell 1996, AJ, 108, 1382.
Slide 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 Slide 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 ) Slide 23 Feb. 16, 2004STScI Star/ISM Journal Club A
pre-main sequnce galore Hillenbrand 1997 1.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 Slide 24 Feb. 16, 2004STScI Star/ISM Journal Club The
initial mass function Hillenbrand & Carpenter 2000 Slide 25
Feb. 16, 2004STScI Star/ISM Journal Club HST/WFPC2 survey in U and
B bands 6 WFPC2 orbits in March 2001 6 WFPC2 orbits in March 2001 4
fields imaged in F336W and F439W 4 fields imaged in F336W and F439W
F336W exposures: F336W exposures: 1 s 30 s 4400 s F439W exposures:
F439W exposures: 1 s 30 s 2180 s Slide 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 Slide 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. Dolphins HSTPHOT package Use A. Dolphins HSTPHOT
package WFPC2 Stellar Photometry with HSTphot, A. E. Dolphin 2000,
PASP, 112, 1383 http://www.noao.edu/staff/dolphin/hstphot Slide 28
Feb. 16, 2004STScI Star/ISM Journal Club Sources we neglect Slide
29 Feb. 16, 2004STScI Star/ISM Journal Club sources we accept
Single, isolated, well subtracted (possibly) point sources
DataHSTphotresiduals Slide 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 Slide 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 Slide 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 Slide 33 Feb. 16, 2004STScI Star/ISM Journal Club 2.
Calculate magnitudes of reddened templates 1. Use Synphot
http://www.stsci.edu/instruments/observatory/snphot.html 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 Slide 34 Feb. 16,
2004STScI Star/ISM Journal Club F336W reddening Slide 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 Slide 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 % Slide 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
Slide 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 Slide 39 Feb. 16, 2004STScI Star/ISM Journal Club
Variability! Slide 40 Feb. 16, 2004STScI Star/ISM Journal Club 4.
Bolometric correction and luminosity Note: colors, effective
temperatures and bolometric corrections must be coherent Slide 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 Slide 42 Feb. 16, 2004STScI Star/ISM
Journal Club HR diagram Slide 43 Feb. 16, 2004STScI Star/ISM
Journal Club Cluster age: ~1Myr Slide 44 Feb. 16, 2004STScI
Star/ISM Journal Club IR excess vs. UV excess Slide 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 Slide 46 Feb. 16, 2004STScI
Star/ISM Journal Club Accretion is present! Slide 47 Feb. 16,
2004STScI Star/ISM Journal Club Source position vs. Trapezium stars
Slide 48 Feb. 16, 2004STScI Star/ISM Journal Club Mass accretion
rates in the HR diagram Slide 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
Slide 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 Slide 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 ) Slide 52 Feb. 16,
2004STScI Star/ISM Journal Club Final considerations PMS models
(with 10 -5 M /yr birthline) look OK in OMC PMS models (with 10 -5
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 ) Slide 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 Slide 54 Feb.
16, 2004STScI Star/ISM Journal Club The initial mass function
Hillenbrand & Carpenter 2000 Slide 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 Slide 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 Slide 57 Feb. 16,
2004STScI Star/ISM Journal Club Further studies Sky &
Telescope, submitted Slide 58 Feb. 16, 2004STScI Star/ISM Journal
Club The Great Orion Nebula Slide 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 Slide 60 Feb. 16, 2004STScI Star/ISM Journal Club
Excess luminosity vs. distance from 1 Ori-C Slide 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. Slide 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 Slide 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 30s @ 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. Slide 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. Slide 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 Its easy to use! Its easy to use!
