NASA Technical Reports Server (NTRS) 19990042134: Airborne Astronomy Program

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Final Technical Report: Airborne Astronomy Program
Grant NAG 2-1074
The (?irc um._t+_Ilar Er_.,_iron,nent of Low .$[as._ St.at Forming R_:gions
Harold M. Butner Principal Investigator
1. Introduction
Since. the 1980"s, our understanding _tbout tlae. inter-relationship bet_veen the col
lapsing cloud e,n\'elopc _nd the d.isk has been gre_.t.ly altered. While the dominar,;
sta.r formatioc, models invoke free. fall collapse _nd _ r-1'5 de.nsity profile, other sr.,:_,
fivrm:_tior, moc]els arc possible. These models invoke either different cloud ._tartin,z
_ond.itior,.._ or the me,-]]_ting effects of magnetic fields to Mter tl_e cloud geomet_?
,_lur_ftg c..:_i:,.psc. To test these models, it Js necessary to understand the envelope'_
physical _itu,:t,rc. The di._covery of disks, l.,_._:d on millimeter observa.tjons around
young stellar objects, however makes a simple interpretation of I,he etnission con,.-
plicat_d. Depending on t.he wa.velec, gth, the disk or the envelope could domina.t:,"
emlss}on fl-om a. st;,.r. In a.dditlon, the discoveIT of planets arourtd other stars ha..-
made understa.ndlng the disk._ in their own right quite importa.nt. Many star form;-.-
tion models predicv diske should tbrrn m_turally as the star is forming. In m_ny case:_.
the information we derb.'e about disk properties depends implicitly on the assumed
e:nvelope properties. How tc, uriderstand the two components am] their intcracti_,;_
with each oth_,, is a key problem of curreat star forrna.tion.
'-]_ separa.I e ,.,ut the two ,.:,..,mponents, it is r_e.cessary (.o observe sources z_t a._._.).'i_'.ty
tff "wavelengtt,_. over _ hj_h spz_ti_l re.solution. As mentioned above: depending o_;
the phy.sici_.l ,:onclitions in the disk a,_d the envelope, each will contribute differrent,
_naouttt:_ of flu:: a.t each measured wavelength. In addition, high spatial resolution
should allow u:._ro resolve the envelope emission. Envelot, e emission typica.lly extcndr
over many huljd,'eds of AU, whereas the disk will be cofifined to a much smaller arc;a.
By ¢ombiaiI_g hi:gh resolution multiw;_velength d_.ta, with radie_t.ive transfer modeb;:
,__le c:._.i_a.ss_s the likely contribution of both the d]sl,, a,_)dthe envelope. The envelope
contribution ,-2omlr_atcs the fa.r-inf'ared emission, wit.h _,_much as 80% of tbe total flu:.:
coming from the <:ool du_t found in the outer por(,ions of the envelope. This emis.<io:_
ca.n bc dete¢.ted and ma.pped with high resolul, it,_ observation:_, .such a_ the Yerl.,,:-_
Far-lnh'_¢Red (FIR) Camer;_ ou 1,oard the Kuiper Airborne Obscrvatory(I(AO). I_
1993 aad 19!)5, we obtained far-infrared (60. 100, 160, 200 micron) irrta..ges for a
number of young _tellar objects (YSOs'I with the KAO prior to the t(AO's shutdov_ :..
In the p,'oposal covered by the grant (NAC,-'2-l.074), we proposed to a_n_dvz_ the
d,-:._,., acquire, a.dditiorxa.I data at other wavelengt.hs for models, t_nd to develope sourc,:
models for the YSOs ,,ndcr stud:,'. Bascd on the results of these models, we bot:,,._,t,:,
,tefi_',a the range of phvsica.t conditions that _re expected m young stellar systems '-'"/_Z-" t(:,
diff"c.."[ant ages. _x.x_,tmass"es. Through the A_'rborne "Astrormmv " prog.r_am. , _e, "were :.d,.1_:._-c<_/
to z_ccomplish ma.t_y of our project goals. HAY 1 0 1_':3
i'_¥--i ,._I.I- ,...-..W.. - • i_i_._ ..'_ Ir_ .._..'.-...."._...". _'-. tLI_'VF]& IlUq_l/I "kJ')fC. UUI(JC').Ull')'){JJJO't A 11"4c[' ",'" "i-,
II. Observational Data Acquired for Source Models
Far-Infrared Images: In l"Y 93 arid FY95, we were awarded two flights each
year 1o srmdy _he envelope arounds low mass protosta.rs in Taurus. Working with
the "_"crkcs FI P_camera, wc obtained data on a total of 13 sources. The Ycrkes FIR.
c_l.rn,era. c:_;t,ta_ined an 60 element array. Our sta.T_dn.x'dobserving method was to dither
the array around the desired source position, and to take a.series of images tbr h_ter
coa.d,.ling. Initial d_,ta., red,tot.loll indicated tha.t Of tile sourccs were compact, as
IIl08t
wc.,uld be expected for low lumitaosity protostars surrounded by an infalling envelope.
Su,'!_ objects will not tend to heat up a lot of the envelope, and what dust is heated
xvi_3be cx_m:entra.'.ed towards the center. However, two sources (l.1527 a.mt LI551NE)
appeared _o show extended emission. This was particularily interesting since these
ol) iect.s maw be the t,he youngest ohjects in the sample. The ell.ira of youth is b;_sed
,:,n their spectral eI_ergy ,tistrlh,tlrms (..qED's), whhq_ ace peakv.d very strongly ixa the
I:IH. Such a pe_.k imt:,!ie:;: tha.t the object is still deeply enshrouded in dust.
Our initial da_.I.;_,ret]uctior, was based on smoothing the data with a relatively
broad :._mooI,F,ing r,,,,ct;on (i.e. a (.;aussian be,.'_m). The _moothing resulted in the
da.t.a being far from tl-,,: diffraction limit. To _ddress this situation, we undertook
I_v:_h the Yerkes group) _o re-reduce the dat:._ using improved convol,.ttio.u methods.
Due to the de_,ire, we had to spend considerable time to ,_chieve the diffraction limit.
'l'in,..-se new results a.re ._till being analyzed, however, _hey confirm the detection of
,::,fended e_r_issi,-_r, a.round L1551NE and L1527. The final models of r.he KAO results
ace still in preparatioT_.
'lb supplemeu.' r.t-,c N:\O data, we obtained observa.t, ion_ a.t rele, t.ed wa.,'el,:_..:4_t ,
for a. laumber of the: som'ccs in our KAO dataset.
Mid-Infi'ared spectra: A large sample of T Tauri stars was studied by Cohe.",
and Witteborn in 1985 a.t l0 pro. To extend this survey, we obtained R=200 spectra
for several T Tauri st.ars, lad a more extended sample of tterbig Ae/Be stars. These
.sta._-._have a variety of 9.8 pm silicate emission. This emission fea,ture reveals that
optically thin sili,:ate dust is in the system. Such dust is similar (spectroscopically)
to dust seen a.ro,,_d some Vega-like objects like Beta Pie.
fhe pa._sage of comet lime Bopp provided a.n opport.unity t,o me_sure t,h_ spec-
l.ro._eopic properties of cornets for compaxison with our '.1.''_.'anri _.r,d l'[erbig Ae/Fle
sample. The comet spectra was found to h:_ve some features that were time variable.
The comet spectra, reveal the presence of grain componenents that. might be pr_.._olar
(b_ed on comparison with IDP spectra). We hope to tie the Comet Hale Bopp work
to our FIR/MIR studies in our final models.
Mid-Infrared images: Using the MIRAC2 (Mid-Infrared Array Camera), we
imaged s,::,eral of the embedded YSOs at 10/,n_. The.se observations provide high
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sensitivity high sp_tlal observations of the circumstell_r environment on _ize _cMes
oF"150 AU. M().-:I; of the observations are consistent with the mid-irtfi'_.red emission as
coming from a disk. Extended emission is possible, since, w_. found several example_
in related studies of Herbig Ae/Bc stars. IIowever, in general, the T T_uri/embcdded
low rna._._ .stars a.re (.oo cool to heat an extended envelope unle._s some: unusual gr_in
heatir_g mechanism is invoked.
We obtained 10 _nd 20 /_na images of the Trapezium cluster, with its proplyds,
which w_: are currentl.y analyzing to provide a_.,:omparison wit.h our isolated st_rs.
I_itia.l result8 a.re being i.,,.,bljshed in Deurscb et al !1999).
Submillinaeter/millimeter photometry: We focused on Taurus embedded
hSOS and the Vega-like s!_r._. In the c;_se of the Taurus sonrces, which includes our
IqAO sample, w-_ have obtained t_complete survey of tl't¢: .150-2000 ,_m etnizsion using
the JCMT 1:3 me.ter telescope. For the: Vega-like stars, wc used the (...'SO 10rn ;_tu:l
IRAM 30m tele._copes to get 8130 and 131)0 Hm photometry. The'data will be writtPn
,.tp in two pa.p(::r:<
S ubmillimet er/tk'Iillimeter lnterferornetry:
A number of our sample stars have ,:t_ta already a.va.ilable in the literature. For
lhose soureeu F_ot already observed, we obtained 1..3 ,r,m interferomctry da.ta for the
t,,-ightest 16 YSOs it, our '1auras sample. Th(-'.:_e obser_'a.tion_ e.-:te_,ded a. previous
survey we had doxte. \.Ve detected 14/1(-; sources {i_Va.lmier e_ el. 1999 in prep). Of
pa.rt.icula.r im;erest, we discovered evi,.1.o.nce for ;x couple of bim_rics in our sg_,'c,ple
(L.t_;51NE). This dat.a, et iu to be combined wit.h published interferometer 2.7 m,',l
data. reported in several surveys. X.Ve also w_.re awarded time to study a sample of
Taurus YSOs v'ith the JCMT-CSO Single-Beam-Int:er{6.ro,,-u-:ter, and got. data on DG
Taxi. among other sourct)s.
Summary: We ha.re, obtained the complete SE;D from 1.0 microns out. to
!.3ram for _ll of our sour(:e_. Vve have the FI/'( imaging da.ta., processed to reveal the
ma.ximm-n _ngular re_ol,,tion pou.qble, which allows us to model the disk. To model
the disk, we have the high resolution millimeter interfe.to,'oetry de.re..
.!.:"../'I.,I , ,, lnn L_v,vmuocooooH !_ u4
111-h.lodeling Techniques Developed for Source Models
At the start of our 14._() research, we had orie primary modeling technique: a 1-D
radiative transfer code that _llowed us to e×plore a variety of density gradients and
gra.b_ propet_.ies. We also developed a. _._ay to including disk emission ia our model.
\Vil h these model._, we can explore 1mtny types of disk/envelope models.
Wc identified two other ra.dia.tive t,'ansfer codes tha.t would be useful for our
mode.Is:
l..) Inclusion of Polycyciic Arums.tic Hydroca.rbons (PAHs) and small grain heat-
ing for the models. "Pllis code, developed by ,Siebemnorgcn, Krugel. _nd Ma.this
(1992), allows u:s to do Spatial mo,iels of the PAIt emission and small grain emission.
Such effects are critical to understanding the emission from a number of the Herbig
Ae/Be stars we have under study.
2.) A Ea.,:t 2-D code: Developed at Jena. by I)r. Men'shchikov, it can ha.nd!e
}:,oth deeply embedded sources as well a.._visible disks. It, has been _pplied by Dr.
Mcn'shchikov to L195! and IlL Tau. We int,ead t(:, apply it _,o our more de,.-.pl,,
,.-:mi:,edded sovrces (L1551N g and L] 527).
Overall. tl'Ler,: are rhr,-ze importar,t paramel, ers we eyamine:
1) The envelope geometry and temperature structure.
This is best d,:,ne u,ith the SED and sp_,tially resolved data at far-infr_red/sub-
_:_illimeter wa,.'el engths.
2) The disk geometry and ternperature structure.
This is mo,t sensit.ive to t,hc mid-Jaffa.red emiseion, due _,othe role of small grain._
or PAHs. tIigh resolut.io1_ data at 10 microns provides the best constraints.
3) The dust properties in both the envelope and the disk.
The model,z a.llow a _radeoff (to a. limited extent) bet,ween dust properties a_d
t,h,'-:inner stucr.ure of the disk/envelope system. However, tt_e presence or absence of
silicates is strongly limited by the I0 micron spectra.
IV. Results to date
Combined with our iuitia.l k'AO prograrn, we find:
1.) The va._t majority of emhcdded YSOs in Taur _._a.re compact at i00 microns.
The models most consist, ent with our data and oLher observations are eithm" domir, ated
l-.y di._k emission (f(.,r ._ou,'ees like (']G 'r'_u) or envelopes that have relatively steep
den._ity gradients (r -15t°-2"°).
2.) The subznillimet, er/millimeLer photomete:," suggests that envelope mod(--Is
(such a.,c those of tl_rtma.nn et aL (1.99a) _re very successful. However, in a. few
cases) they are clearly missing _ component in their models. Divk emission ply', an
irnporta.nt rote and mu,*t be considered when predicting the overa.]l arnis._icm. (Burner
e_ aI. 1999b(in prepara.1]on)}.
;j) In the t.wo ca.._es where we seem to have extended emission, we have to inve.sti-
ga.tc other possible source models than a Sh_t collapse. This work is still i,t t)rogress.
\Ve will cous;dering models such _s those ()f Ha.rtmann el. al. (1995), which invoke a
flat _:heet rather tha.x._spherical colla.i)se.
V. Future "Work
We still dolt,:,, the final modeling fi_r the revised FIR maps, and a.nticipat_" havin:_,
*we or three papers done hy the end of the year. These papers will present our da.l.;,.
and the complete -cer of parameter space that we explore. In particular, we wish
to assess the role of fla.t sheet (:vllapse mo,-lels (.-:ee point ?, above) in expla:ining our
.Ta,rus t"ll_ do.ta.
_.V--_FI--'.J'._._._ iU:" ' L.nV Vrl _.'.,u'm'rm._ ,_
]L. JlIP, PIU_ ,,)_-UULU,.),3UH .............
VI. Papers in Preparation or Published
The foliow/ng papers were supported in part by the Airborne Astronomy Grant
NAG 2-1074. The support provided salary, travel funds, or equipment used tbr data
reduction a.nd a.nal:.'sis
Refereed Articles
H..J. Wa.lker, V. Tsikoudi, C. A. Clayton: T. Gcballc:, I). H. Woodert, & H. M. Butner,
"The Ntmare of the unusual source IRAS 18530+0817," 1997. A&'A. a23,/112.
H. M. Butner, H..J. Walker, D. II. Wooden, & F. C. Witteborn, "1997: Examples of
Comet-Like Spectra Among _ Pie-Like Stars, in Astronomical at_d Biochemir.:al
O'ri,jins" arm tl_e Search for Life in the Urdwr, e..,ed. C. B. Cosmovici, S. Bowyer,
,._zD. Werthimer t,Bologna: Bditrice Comt,ositori), p.149.
G. H..Moriarty-Schieven & H. M. Burner, "A Sub-*'lillimeter-W_ve 'Flare' From GG
Tau'::" t.q.c.:)7,Ap. J., 474, " "¢'
Selectee] Unrefereed Articles
:\ Natta, & II. 13uther, "Re._olving Disks in YSOs." 1996, in lr(rare'd SlmVe: Irde:,-
.fcrow..etry. ed. A..,Ubc,di, T. dc Graauw, C. Eiroa, C. J. Scha.linski, am] H.
Thro_son (.ql:,a,:e Science ReviP.ws), in press.
Papers in Preparation
i-1 _l Burner. (;. 1I..Moria.rt.v-Schievcn. P. Wannier, '"Spectral Euergy 13isT,ributions
ir_ Ta.urus, 1999, Ap..L, in preparation.
H. M. Butner, ¢-; M. Mon;_rty._,;tneve, t, ,:l. al. "FIR. Imaging of Low Me_ss Sources
in 'Tau,'_s," lq99, ,,l.p.d._ i_t prepara.t;on.
L Is:. Deutsch, M. t,[aasi.s, N. Smith: J. I. Hera, G. G. Fa.a;o: H. M. Butne,', W. t".
Hoffman, A. Day,l, "Widl:.--Fh.'ld Thermzd Imaging or l.hc. Orhm Nebula at High
Spatial Resolution :' ]999, Ap../., in prepc_ration.
i-'. C;. "xXra,nnier, J. Keenc. (.;. Moria.rty-Scl._ieven, and H. M. Burner, '.1..3 MM inter-
ferometry of Taurus Sottrce._(' 1999, Ap..1., in prep,.xr,-,tion.
D. II. _,Vooder,, FI. M. Burner, &: g. (' Witteborn, "'A Mid-hffra.red Survey of T '_Pauri
Stars." 2999, Ap. J., it, preparation.
_nl u_ oo t\_ ]_'.dr_.-.... _:Iv II-r- rMA I_U. :DdUOdO_Joq _ .U,
7
References
Below we include the references for _rticles mentioned in our report..
But.nor, H. M.. Wa.lkc.r, H..I, Wooden, D. H., &: Wittebor.0, F. C. 1997, in Ast, ronom-
ica[ and Bi_.,ch,:mical Ori9in._. arid the....S'earch for Life" in th.c Univcrsc, ed. C.. B.
Cosmovici, S. Bowyer, & D. Wcrthimer (Bologr_a: l_]ditrice Compositorl), p.149.
P,utner, n. M., _,:_:zt]l<.ttr: H, J._ Wooden, D. II., & "vVitteborn, F. C. 199.9a, Ap..]., iz_
prepar_ior_.
Butner, H. M.. Moriart, y-Schieven, G. H., and Wttnnier, P. 1999b....lp.J., in pr_p_.,a-
1.ion.
Co} en, M., Wit.reborn. F. C' 1985, Ap.], 294, 345.
Deuts,=h. b. I(.. ltora. J. L., Butner. H. M.. l-].offmann, \:V. 1"., ,_,"Fa.zio. G. G. 1995
in (::irc_msbllar Matter _19.9._,ed. G. D. Wa.tt (Kluwer Dordrecht), p.89.
I-Iartmann, L, t,:ea.v,:m. S..I., _nd CMvct, N. 199::L Ap.J, 407. 219.
Ha.rtrnann. L.: Calvet.. N., aml Boss. A. 1996_ .,4p..L, 464, ,387.
_larsh. 1£. A.. and Mahonev,. M. ,l. lC"_),9.. A pJ, ..,._-gs..L,115.
5lori_._rty-.S_chieve_l, C. H. and Burner, H. M. 1997, Ap. J., 47"4, 76S.
W,:,,:,d,_n, D H.. t3,__tner, H. M., _- \.Vitteborn, F. C. 1.9.99, ,-IT)..]., in preparation.
Wannier, P. (].._ t<eene. J., Moriarty-Schievcn. Butner,.F1 ....M. . I9(t,.1...,Ap. J., in l:,rep_.,-
raI.iO[l.