V1647 Orionis: Reinvigorated Accretion and the Re-Appearance of McNeil's Nebula

1.3 MB·English

by  Colin Aspin

Version: January24,2009
PreprinttypesetusingLATEXstyleemulateapjv.10/09/06
V1647 ORIONIS: REINVIGORATED ACCRETION AND THE RE-APPEARANCE OF MCNEIL’S NEBULA
Colin Aspin1, Bo Reipurth1, Tracy L. Beck2, Greg Aldering3, Ryan L. Doering4 Heidi B. Hammel5,9,
David K. Lynch6,9, Margaret Meixner2 Emmanuel Pecontal7, Ray W. Russell6,9, Michael L. Sitko8,9,
Rollin C. Thomas3, Vivian U1
Version: January 24, 2009
ABSTRACT
9 In late 2003, the young eruptive variable star V1647 Orionis optically brightened by over 5 mag-
0 nitudes, stayed bright for around 26 months, and then decline to its pre-outburst level. In August
0 2008the star was reportedto have unexpectedly brightened yet again and we herein present the first
2 detailed observations of this new outburst. Photometrically, the star is now as bright as it ever was
followingthe 2003eruption. Spectroscopically,apronouncedPCygniprofileis againseeninHαwith
n
a an absorption trough extending to –700 km s−1. In the near-infrared, the spectrum now possesses
J very weak CO overtone bandhead absorption in contrast to the strong bandhead emission seen soon
0 after the 2003 event. Water vapor absorption is also much stronger than previously seen. We discuss
1 the current outburst below and relate it to the earlier event.
Subject headings: stars: individual (V1647 Ori) — circumstellar matter — stars: formation

]
R
S 1. INTRODUCTION served rise in optical brightness of around 5–6 magni-
. When V1647 Orionis went into outburst in the fall tudes,ii)anopticalspectrumindicativeofaG-toF-type
h
supergiant star, iii) a NIR K-band spectrum typical of
p of 2003, it brightly illuminated a monopolar reflection
a M-type giant, iv) the star remains in an elevated state
- nebula subsequently designated McNeil’s Nebula (Mc-
o Neil 2004). The young star itself increased in optical for many years, even decades – FU Ori has declined lit-
r and near-IR (NIR, K-band) brightness by around 5 and tle inoverthe 70yearssinceits discovery(Herbig(1966,
st 3 magnitudes,respectively,andsparkedaworld-wideef- 1977),v)anHαlineinemissionwithanassociatedblue-
a shifted absorption component (i.e. a P Cygni profile),
forttostudy the detailsofthis raretype oferuption. To
[ and vi) an associated, generally curving, reflection neb-
date, this has resulted in over 50 research papers which
ula. What has been gleamed with regard to V1647 Ori,
1 relatethe characteristicsofthe starandnebulafromthe
however, is somewhat contradictory to these definitive
v time of its detection to the time when it had faded to
8 its pre-outburst optical brightness (in February 2006). characteristics in that it had a relatively short outburst
3 The reader is referred to the most recent publication on period (approximately 26 months), its optical and NIR
3 outburst spectra possessed strong atomic and molecu-
V1647Ori,(Aspin, Beck,& Reipurth 2008,ABR08), for
1 lar emission features, and the eruption was shown to be
a comprehensive list of previous work.
. repetitive–Aspinetal. (2006)describedanearlierevent
1 It has been speculated that V1647 Ori may be a new
commencingin1966. Suchpropertieshavemoreincom-
0 example of the class of young variable stars designated
9 “FUor” after the class progenitor, FU Orionis (Am- monwith thoseobservedinthe “EXor”classoferuptive
0 bartsumian 1971). Only about ten so-called “classical” variables, named after their class progenitor, EX Lupi
: FUors, (those that have been directly observed to op- (Herbig 1989).
v
It was expected that the next eruption of V1647 Ori
i tically brighten over a period of a few weeks to a few
X months) have so far been found. A comprehensive re- would be ∼37 years after the 2003 event, assuming the
timescale between the 1966and 2003events wastypical.
r view of the properties of FUors was given by Hartmann
a However,in late-August 2008,some 18 months after the
&Kenyon(1996),however,itis importantto relatehere
fading of the 2003 outburst, V1647 Ori was observed to
the main characteristics defining this group. i) an ob-
brightenbyaround5magnitudesyetagainandMcNeil’s
1InstituteforAstronomy,UniversityofHawaii,640N.A’ohoku Nebula became brightly visible (Itagaki et al. 2008).
Place,Hilo,HI96720. E-mail: [email protected] This was confirmed by Aspin (2008) who showed that
2SpaceTelescopeScienceInstitute,3700SanMartinDrive,Bal- V1647 Ori had brightened in the red optical (∼6500 ˚A)
timore,MD21218.
3Lawrence Berkeley Lab, Physics Div., MS-50/232, One Cy- from r’=23.3 in March 2006 to R=17.3 in late-August
clotronRd.,Berkeley,CA94720, USA 2008. HerewepresentnewopticalandNIRobservations
4DepartmentofPhysicsandAstronomy,ValparaisoUniversity, ofV1647Orifromlate-Augustto early-September2008.
Va5lpSapraaciseo,ScINien4c6e38In3s.titute, 4750 Walnut Street, Suite 205, Boul- In § 2 we briefly describe the observations and data re-
duction. In § 3 we present the results, while in § 4 we
der,CO80301.
6TheAerospaceCorporation,LosAngeles,CA90009. discussthecurrenteventinrelationtothe2003outburst.
7Observatoire de Lyon, 9 Avenue Charles-Andre, 69561 Saint-
Ge8nDis-eLpaavratmlCenetdeoxf,PFrhaynscices, University of Cincinnati, Cincinnati 2. OBSERVATIONSANDDATAREDUCTION
OH45221. Belowwepresentnewdatatakenonfourdifferenttele-
9VisitingAstronomer, NASA InfraredTelescope Facility, oper-
scopes and with five different instruments. Optical R-
atedbytheUniversityofHawaiiundercontractwiththeNational
AeronauticsandSpaceAdministration. bandimages(seeFig.1)wereobtainedontheUniversity
ofHawaii(UH) 2.2meter telescopeonUT 2008Septem-
2 Aspin et al.
Fig. 1.—TheregionimmediatelysurroundingV1647OrionisandMcNeil’sNebulaatthreedifferentepochs. Theleftimagewastakenin
anSDSSr’filterin2004,aroundoneyearafterthe2003outburst. Themiddle-leftimagewastakeninastandardJohnsonRfilterin2007,
around 10 months after V1647 Ori had returned to its pre-outburst optical brightness. The middle-rightimage was taken inthe sameR
filterin2008,soonaftertherecentbrighteningofthestarandthere-appearanceofMcNeil’Nebula. Therightimageisadifferenceimage,
2008–2004. In this image, white is more flux in 2008, black is more flux in 2004. We note that V1647 Orionis is the point-like object at
theapexofthemonopolarreflectionnebulaextending northward. Theimageswerescaledtoresultinthecancellationofthefaintbinary
staratthebottom oftheimage.
ber1usingtheTektronix2K×2KCCDcamera(Tek2K). al. 1998) using broad N’ (λ =11.2 µm) and narrow
c
The on-source exposure time was 120 seconds and see- Qa (λ =18.30 µm) filters. Conditions were clear, dry
c
ing was ∼0′.′7. The images were calibrated by using a andstable throughoutthe observationsandphotometric
sequence of six field stars described in Aspin, Herbig, & calibration was performed using similar observations of
Reipurth (2009, henceforth AHR09). the bright “Cohen” standard star (Cohen et al. 1999)
Optical images were also obtained on Gemini-South HD39400 (N’=1.534, Qa=1.434).
using GMOS (Davies et al. 1997; Hook et al. 2004) on Near-IRimageswereobtainedontheWIYN3.5-meter
UT2008September22. TheSDSS g’,r’,i’,andz’filters telescope on UT September 16 2008. The WHIRC NIR
were used and the on-source exposure times were 240, camera (Meixner et al. 2008) was used with standard J,
120, 120, and 80 seconds, respectively. Details of the H, and Ks filters. Flux calibration was achieved using
photometric calibration, can be found AHR09. Seeing observations of the UKIRT faint standard star FS 07
during the observations was ∼0′.′6. (Hunt et al. 1998).
Optical spectroscopy was obtained on the UH 2.2 me-
ter telescope on UT 2008 August 31 using the dual- 3. RESULTS
channel integral-field unit (IFU) spectrograph, SNIFS
(Aldering et al. 2002; Lantz et al. 2004). The 6′′×6′′ In Fig. 1, we show a comparison of red optical images
of V1647 Ori from three different epochs. The left im-
field-of-view of the SNIFS spectrograph is filled with a
age is from UT 2004 September 3 and was taken with
15×15gridoflenslet-definedspatialelements,eachsam-
an SDSS r’ filter using GMOS. This was around 10–11
pling ∼0′.′4. The data was reduced by the SNIFS reduc-
months after the 2003 outburst of V1647 Ori was first
tion pipeline (Aldering et al. 2006). The spectral reso-
detected(McNeil 2004)andV1647Orihada magnitude
lution of the final spectrum was R∼1850 which was ex-
ofr’=17.8. The middle-leftimageshowsthe sameregion
tractedfromtheIFUcubeusingawavelength-dependent
of sky but was taken on UT 2006 December 22 using
PSF fitting procedure (Aldering et al. 2006). Wave-
a Johnson R filter with the UH Tek2K camera. At the
length calibrationwas performed using the SNIFS inter-
timeoftheseobservations,V1647Orihadbeenatitspre-
nal calibration unit and flux calibration was performed
outburst(redoptical)brightnessofr’=23.3foraround10
using observations of spectrophotometric standards.
months. The middle-right is our recent UH Tek2K im-
An optical spectrum was also obtained on Gemini-
age detailed in § 2 above. In this image, V1647 Ori has
South using GMOS on UT September 22. We used the
R400 grating and a 0′.′75 slit giving an effective spectral anopticalbrightnessofR=17.3. Comparingtheleftand
middle-rightimages,wenotethatinbothV1647Oriand
resolutionofR∼1900. Datawastakeninnod-and-shuffle
itsassociatednebulaarestronglyvisible. However,inthe
mode to aid in the removal of the bright red optical sky
middle-left image both the star and the nebula are only
emission lines.
faintly visible. The bright knot visible in the middle-left
NIR spectroscopy was obtained on the NASA IRTF
image (top and left of center) is the Herbig-Haroobject,
telescopeonUT2008September4usingthefacilityNIR
HH22. WenotethattheopticalbrightnessofV1647Ori
spectrograph SpeX (Rayner et al. 2003). The cross-
in the 2004 and 2008 images is similar as is the bright-
dispersed (XD) mode was used and observations were
ness and morphology of McNeil’s Nebula. The far-right
acquired in both the short- and long-XD settings. The
image shows the difference between the 2004 and 2008
datawerereducedusingtheSpeXIDLpackage(Cushing,
imageswith white implying that the objectwasbrighter
Vacca,&Rayner2004). Telluriccorrectionandfluxcali-
in 2008, and black meaning brighter in 2004. The im-
brationwereperformedusingthe A0Vtelluricstandard
ages were scaled prior to subtraction to give the same
star HD 39985. Conditions were clear and the seeing
signal in the faint binary system near the bottom (and
stable during the target and standard observations and
leftofcenter)oftheimages. Clearly,therearesignificant
hence we consider the flux calibration good to the 10%
differencesinbrightnessbetweenthetwoepochssuggest-
level.
ingthat in2008,the reflectionnebula is illuminatedina
Mid-IR(MIR)imagingwasobtainedonGemini-South
somewhat different manner than in 2004. This suggests
on UT September 13, 2008 with T-ReCS (Telesco et
thatdustobscurationcloseto V1647Orimayplayaim-
V1647 Orionis, reinvigorated 3
Fig. 2.— Optical spectra of V1647 Ori from three epochs, UT August 31, 2008, February 21, 2007, and October 6, 2004. The 2008
spectrum is fromthe latest outburst ofthe star whilethe 2004 spectrum was taken duringthe 2003–2006 event. The 2007 spectrum was
takenaroundoneyearafterV1647Orihadreturnedtoitspre-outburstopticalbrightnessafterthe2003eruptionhadsubsided. Notethe
2004spectrumdidnotincludetheCaIIlines. Theleftthreepanelsshowthefullspectrarangeobservedwhiletherightthreepanelsfocus
ontheregionimmediatelyaroundtheHαemissionfeature.
portant role in defining the observed morphology of the
nebula. TABLE 1
Photometry of V1647Ori
Photometric observations of V1647 Ori from the opti-
cal through mid-IR are shown in Table 1. Optical and
Filter(λ) UT 2008Fluxa 2004Fluxb
NIR colors are also given. Within the associated uncer-
(µm) (mags) (mags)
tainities, the optical through NIR brightness values for
V1647OriarecomparabletothosemeasuredinFebruary gV’((00..5457)5) 22000088//0098//2321 1198..8160±±00..1125 1280..5005±±00..1155c
2004 when the source was last observed to have bright- r’(0.63) 2008/09/22 17.53±0.07 17.70±0.09
ened significantly (Reipurth & Aspin 2004). i’(0.78) 2008/09/22 16.03±0.06 15.90±0.08
We present our new optical spectrum of V1647 Ori in z’(0.925) 2008/09/22 14.43±0.06 14.39±0.06
J(1.25) 2008/09/16 10.62±0.07 10.85±0.10c
Fig. 2 (bottom). We additionally show similar spectra H(1.65) 2008/09/16 8.90±0.07 8.90±0.10c
fromOctober2004(top)andFebruary2007(middle)for Ks(2.2) 2008/09/16 7.53±0.07 7.60±0.10c
directcomparison. InOctober2004,V1647Oriwassome N’(11.2) 2008/09/13 2.51±0.20 1.50±0.20
11–12 months into its eruption and had not yet started Qa(18.3) 2008/09/13 0.62±0.20 –
g’-r’ 2008/09/22 2.33±0.17 2.35±0.12
to decline in optical brightness. In February 2007, the
r’-i’ 2008/09/22 1.50±0.10 1.80±0.09
star had been at its pre-outburst optical brightness for r’-z’ 2008/09/22 1.60±0.10 1.51±0.08
around 1 year. In all three spectra, Hα is in emission J-H 2008/09/22 1.72±0.10 1.95±0.14
although only in October 2004 and August 2008 did it H-K 2008/09/22 1.37±0.10 1.30±0.14
show a blue-shifted absorption component (a P Cygni
a Data acquired during the current outburst.b Data acquired in
profile). Onboththesedates,theblueshiftedHαabsorp- Feb–Mar2004.c DatafromMcGeheeetal. (2004).
tionextendedtoapproximately–700kms−1 althoughin
August 2008 the depth of the absorption is less than in are details of the optical spectral features present. Two
October 2004. The full-width half maximum of the Hα lines that are conspicuously absent are the [S II] lines at
emissionislargewiththelinewingsextendingtoaround 6717 and 6731˚A which were present in February 2007.
±1000kms−1. Thisissomewhatlargerthanobservedat This is likely due to the already weak lines (see ABR08)
thestartofthe2004event(i.e. ∼750kms−1,seeAHR09 being masked by the addition of strong continuum (ac-
for more details) suggesting the physical conditions in cretion) emission which was not present in the February
the Hemissionregionaresomewhatmoreextreme. Also 2007 spectrum. Finally, we note that the SNIFS acqui-
presentintheAugust2008spectrumaretheCaIItriplet sition image of V1647 Ori gave a magnitude of V=18.1.
lines in emission. The ratios ofthese lines (1.6:2:1.7)are Fig. 3 shows the SpeX NIR spectrum of V1647 Ori
similar to those found in February 2004 (1.5:2:1.7) im- (bottom). As in the optical, we also show spectra from
plying that unlike the emission seen in February 2007 two other epochs, in this case, February 2007 (middle)
(with ratios 1.7:2:1.9), conditions in the Ca II emission and December 2004 (top). Present in the August 2008
region have become optically thick producing saturated NIR spectrum are the atomic emission lines of He I
line emission. The Ca II emission lines are discussed in (1.083 µm, P Cygni profile), Paβ (1.282 µm), weak
more detail in ABR08. Also present in our recent spec- [Fe II] (1.644 µm), He I (2.058 µm, P Cygni profile),
trum are O I (6300 ˚A) in emission, and O I (7773 ˚A) Brγ (2.166 µm), and Br α (4.051 µm). Details of these
in absorption. Other weak features may be present but, featuresaregiveninTable2. ThemolecularCOovertone
with the spectral resolution obtained with SNIFS, it is bandheads longwards of 2.294 µm are weakly in absorp-
difficulttodetermineiftheyarereal. IncludedinTable2 tioninbothFebruary2007,veryweaklyinabsorptionin
4 Aspin et al.
Fig. 3.—The NIR 1 to 4.2 µm SpeX spectrum of V1647 Ori taken on UT August 31, 2008 (bottom panels). For comparison, wealso
showthesamewavelengthrangefromSpeXspectrafromUTFebruary21,2007(middlepanels)andUTDecember10,2004(toppanels).
The main spectral features are identified. Features present are water vapor absorption bands (in J, H, and K), water ice absorption (at
3µm),andemissionlinesofPaβ(at1.282µm),weak[FeII](at1.644µm),HeI(at2.058µm),Brγ(at2.166µm),andBrα(at4.051µm).
Therightthreepanels zoom into theK-bandregionofthe threespectra. Notethe CObandheads (at2.294 µm)areinemissionin2004,
areweaklyinabsorptionin2007,andperhapsveryweaklyinabsorptionin2008.
fittheFebruary2004datawithatemperatureof<20K.
TABLE 2 Their conclusion was that the line-of-sight CO ice had
SpectralFeatures
not been thermally processed and was consistent with
that found towards quiescent dark clouds and region of
λ Line Wλ Flux Comment
(µm) ID (˚A) (Wm−2µm−1) low-mass star formation. A qualitative comparison of
(10−17) the band shape in our August 2008 spectrum with that
in the February 2004 spectrum of Vacca et al. (2004)
0.6300 OI –1.1 0.02 –
0.6563 Hα –39/+1 0.89 PCygnia suggests that little has changed in the characteristics of
0.7773 OI +5 – – the CO ice absorption in the intervening four years.
0.8498 CaII –7 1.26 – Using the Paβ and Brγ line fluxes, we can es-
0.8542 CaII –8 1.60 – timate mass accretion luminosities (L ) and rates
01..80686320 CHaeIII –2–/6+7 11..5355 PCy–gnib (log(M⊙ yr−1)) in a manner similar toatchcat presented
1.2818 Paβ –6 8.91 470kms−1c in ABR08. Using the relationships defined by Muzerolle
1.6444 [FeII] –0.3 0.91 veryweak et al. (1998) and Gullbring et al. (1998), we find that
2.0581 HeI –1/+2 3.98 PCygnid inAugust2008the linefluxesshowninTable2,resulted
2.1659 Brγ –5 18.6 665kms−1c in values of Lacc=1.42 L⊙ and log(M⊙ yr−1)=–6.28 for
24..20954009 BCrOα –+110 35–.5 we4a1k5bkamndsh−e1acds Paβ,and Lacc=12 L⊙ andlog(M⊙ yr−1)=–5.34for Brγ.
4.6741 COice +57 – 830kms−1c This assumes a stellar temperature of Teff=3800 K, a
stellar luminosity of L∗=4.9 L⊙, and an inner radius for
a FWHM=450 km s−1, absorption to –950 km s−1, minimum at – the accretion disk of Rin=5 R∗ as in ABR08. For the
690kms−1,redtailto+830kms−1.b FWHM=320kms−1,absorp- August 2008 fluxes, we also assumed a visual extinction
tcioomnptoon–e7n6t.0dkFmWsH−M1,=m4i0n0imkumms−at1,–a3b00sokrpmtios−n1t.oc–F8W50HkMmosf−e1m,imssiinoin- ofAV=6magnitudes. Thiswasdeterminedbyderedden-
mumat–290kms−1. ingtheobservedNIR(J-HandH-K)colorsofV1647Ori
to typical T Tauri star values as in ABR08 (see their
Figs. 13 and 14). We note that the values of L and
acc
August 2008, while in October 2004 they were strongly log(M⊙ yr−1)derivedfromPaβ andBrγ areinconsistent
in emission. The water vapor absorption bands, at 1.4,
being larger from Brγ by factors of ∼8 and ∼9, respec-
1.9, and 2.5 µm, are strongly in absorption, and appear
tively. NovalueofA resultedinsimilarvaluesfromthe
V
muchdeeperinAugust2008thanineitherFebruary2007
twolines. Wecanperhapsattributethisdifferencetothe
or December 2004. The other broad feature seen in Au-
emission in Paβ being optically thick while in Brγ the
gust 2008 is the water ice absorption band, centered at
emission is less so. The ratio of the dereddened (A =6)
V
around 3 µm. It appears somewhat different in shape in
fluxes,Paβ/Brγ,is ∼1which,fromthe observationsand
August2008withrespectto the twoearlierspectrawith
analysisshowninFig.15fromMuzerolleetal. (2001),is
a less rounded minimum and a more gradual increase
afactor∼5×smallerthanthatobservedintypical’quiet’
back to the continuum on the long-wavelength side. Fi-
classical T Tauri stars. We note that in February 2007,
nally, the August 2008 spectrum shows the presence of
when V1647 Ori was supposedly in quiescence, ABR08
the 4.674 µm CO ice absorption band (not included in
derived values of ∼4 L⊙ and ∼–6 (using the same phys-
the plot shown in Fig. 3). This band was previously ob-
ical parameters as above with A =19) from both lines,
V
served in V1647 Ori by Vacca et al. (2004), Rettig et
and a line ratio of ∼5. Clearly, the changes observed in
al. (2005), and Gibb et al. (2006). Rettig et al. mod- Lacc and log(M⊙ yr−1) warrant a more detailed investi-
eled the band shape using polar, and apolar CO ice and
gation.
found that a predominantly apolar CO matrix ice best
V1647 Orionis, reinvigorated 5
Our MIR imaging of V1647 Ori showed only a point Our qualitative interpretation of the results presented
source and hence, is not explicitly presented here. How- above (for the current eruption, the appearance of
ever, we have extracted photometric values from these V1647 Ori in 2007 as described by ABR08, and for the
data and can compare them to earlier measurements. October 2003 eruption as described by AHR09) can be
We find that the integrated flux from V1647 Ori at summarized as follows. We believe that the massive ac-
N’ and Qa is 3.8 and 6.6 Jy, respectively. Similar cretion event that occurredin 2003 did not actually ter-
observations of V1647 Ori in February 2007, when the minatein2006aspreviouslydiscussed,butonlydeclined
star had faded to its pre-outburst optical brightness, in intensity. This is supported by the high-level of ac-
gave N’ and Qa fluxes of 0.23 and 0.44 Jy, respectively cretion found in February 2007 by ABR08, specifically,
(ABR08). Earlier measurements quoted by Andrews, log(M⊙ yr−1)∼–6. We suggest that the ∼6 magnitude
Rothberg, & Simon (2004) showed V1647 Ori to have optical fading of V1647 Ori between late 2005 and early
a 11.3 µm flux of ∼10 Jy. The latter observations were 2006 was the result of not only a factor 10× reduction
takensoonafter the sourcewasdiscoveredby J.McNeil, in accretion luminosity (Muzerolle et al. 2005 derived
specifically, in March 2004. Our N’ flux of 3.8 Jy is a a value of –5), but also the reformation of dust in the
factor of 2.6× smaller than the 2004 outburst value and immediate circumstellar environment of the star which
16.5× larger than the quiescent phase flux. At 18.6 µm had been sublimated by the intense radition field from
(Qa) our flux measurementfrom September 2008is 15× the 2003 accretion burst. We add further support for
the flux observed in 2007. Thus, the ratio of N/Qa thisspeculativeinterpretationbynotingthatthechange
flux in September 2008 is the same (within the associ- in A observed between December 2004 and December
V
ateduncertainities)asinFebruary2007ataround0.55×. 2005 (see Fig. 14 of ABR08) was of a similar order. In
early 2008, we consider that a second burst of accretion
again sublimated circumstellar dust and resulted in the
4. SUMMARY current ∼6 magnitude brightening of V1647 Ori.
What we can conclude about the late-August 2008
Acknowledgments Based on observations obtained
reappearence of V1647 Ori and McNeil’s nebula is that:
atthe GeminiObservatory,whichisoperatedbytheAs-
Inthe optical,V1647OriandMcNeil’s Nebula appear
sociationofUniversitiesforResearchinAstronomy,Inc.,
photometricallyandmorphologicallysimilartowhenthe
under a cooperative agreement with the NSF on behalf
source was first observed in 2004 i.e. shortly after the
oftheGeminipartnership: theNationalScienceFounda-
eruption occurred.
tion (United States), the Science and Technology Facili-
IntheNIR,V1647Oriappearsphotometricallysimilar
ties Council (United Kingdom), the National Research
to February 2004. Spectroscopically, unlike at the start
Council (Canada), CONICYT (Chile), the Australian
ofthe 2003event,CO overtoneemissionis notobserved.
BrγandPaβ emissionarehoweverpresent. Strongwater ResearchCouncil(Australia),Ministrio daCincia eTec-
nologia (Brazil) and SECYT (Argentina). CA acknowl-
vapor bands are also seen.
The values ofLacc and log(M⊙ yr−1) derivedfrom the edges the AAS for financial support. BR acknowledges
dereddened Brγ flux (12 L⊙ and -5.3, respectively) are partial support from the NASA Astrobiology Institute
under Cooperative Agreement No. NNA04CC08A.
of a similar order to those found soon after the 2004
outburst (Muzerolle et al. 2005).
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