Subm itted to A pJ Letters
IR A S 05436{0007 and the E m ergence of M cN eil’s N ebula
arXiv:astro-ph/0403667v1 29 Mar 2004
Bo R eipurth1
Institute for A stronom y,U niversity ofH awaii,2680 W oodlawn D rive,H onolulu,H I 96822
[email protected]
and
C olin A spin2
G em iniO bservatory,670 N orth A ‘ohoku Place,
U niversity Park,H ilo,H I 96720
[email protected]
A B ST R A C T
W e present a study ofM cN eil’s N ebula,a new ly appeared re ection nebula
in the L1630 cloud, together w ith photom etry and spectroscopy of its source.
N ew IR photom etry com pared to earlier 2M A SS data show s that the star has
brightened by about 3 m agnitudes in the near-infrared,changing its location in
a J-H /H -K 0 diagram precisely along a reddening vector. A G em iniN IR IK -band
spectrum show sstrong C O -bandhead em ission and Br isin em ission,indicative
ofstrong accretion. A G em iniG M O S opticalspectrum show sonly a red,heavily
veiled continuum , w ith H strongly in em ission and displaying a pronounced
P C ygnipro le,w ith an absorption trough reaching velocities up to 600 km s 1.
T his im plies signi cant m ass loss in a powerfulw ind. H owever, no evidence is
found forany shocks,ascom m only seen in collim ated out ow sfrom young stars.
A pparently the eruption has dispersed a layer of extinction and this, together
w ith the intrinsic brightening ofthe IR A S source,has allowed an earlier out ow
cavity to be ooded w ith light,thus creating M cN eil’s N ebula.
Subject headings: stars: form ation | stars: pre{m ain-sequence | R e ection
nebulae | ISM :individual(M cN eil’s N ebula) | stars: variables: other
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1. Introduction
W ide- eld photographic and C C D im ages have docum ented the presence ofnum erous
sm allcom pact re ection nebulae in star-form ing dark clouds. Such nebulae m ay possibly
represent a transitionalstage in w hich a young star goes from being an em bedded infrared
source to a visible T Tauristar or H erbig A e/Be star. T his process is w idely believed to
involvepowerfulbipolarout ow activity,asre ected in them orphology ofthenebulae,w hich
are often com etary,w ith the partially em bedded star illum inating an out ow cavity. W hen
observed over longer tim e-scales, such sm allre ection nebulae are often found to vary in
brightness and occasionally in illum ination pattern. Perhaps the earliest know n exam ple is
N G C 2261,w hich re ectslightfrom the young starR M on and wasfound to vary by H ubble
(1916). M ore recently,C ohen et al. (1981) dem onstrated the variability ofthe fan-shaped
nebula em anating from PV C ephei. A tsom e stage,the out ow activity ofa starforthe rst
tim e punches a hole in its surroundings,suddenly allow ing a beam oflight to sweep across
the surroundings. Subsequent eruptions in the source w illagain ood the out ow channel
w ith light. T he em ergence ofthe nebula R e 50 in the Lynds 1641 cloud near the em bedded
source IR A S 05380{0728 was docum ented by R eipurth & Bally (1986). A nother case m ay
have been the nebula IC 430 in L1641,w hich atpresent isquite sm all,butatthe end ofthe
19th century appears to have been a very large and m uch brighter object (Pickering 1890;
Strom & Strom 1993).
2. O bservations
T heobservationspresented below weretaken on the"Frederick C .G illett" G em iniN orth
Telescope1,on M auna K ea,H awaiion U T datesFebruary 03 (near-IR )and 14 (optical),2004.
T he near-IR im aging and spectroscopy was acquired w ith the facility im ager/spectrom eter,
N IR I,using the f/6 cam era giving an im age scale on the A laddin InSb 1024x1024 detector
of0.116"/pixel. Im ages in J,H and K 0 were obtained in totalon-source integration tim es
of3.6 seconds (0.18 seconds,10 coadds,two spatialpositions) in each lter. T he data were
calibrated using sim ilarobservationsofthe U K IRT faintstandard starsFS113,119 and 135.
T he spectroscopic data were acquired using a 0.5" w ide long-slit and K -band grism w ith a
1
B ased on observations obtained at the G em ini O bservatory, w hich is operated by the A ssociation of
U niversities for R esearch in A stronom y,Inc.,under a cooperative agreem entw ith the N SF on behalfofthe
G em inipartnership: the N ationalScience Foundation (U nited States),the Particle Physics and A stronom y
R esearch C ouncil (U nited K ingdom ), the N ational R esearch C ouncil (C anada), C O N IC Y T (C hile), the
A ustralian R esearch C ouncil(A ustralia),C N Pq (B razil),and C O N IC ET (A rgentina).
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totalon-source integration tim e of60 seconds (30 seconds,1 coadd,two spatialpositions)
resulting in a spectrum w ith resolving power 780 covering the wavelength region 2.05-2.45
m icrons. Telluric feature correction was perform ed using observations of the A 0 V star
H IP28056.T he opticaldata were acquired using the facility opticalm ulti-objectspectrom eter,G M O S-N .Im agesin the G M O S Sloan g’,r’,i’and z’ lterswere obtained w ith exposure
tim esof60 secondsand 10 seconds,theshorterexposure tim ebeing used to give unsaturated
im ages ofthe young star. T he G M O S spectrum was a 5 m in exposure obtained using the
R 831 grating,0.5" w ide long-slit,and a centralwavelength of5800 A resulting in a spectrum
covering the wavelength range 4800-6800 A ata resolving powerofR 4500.Infrared im ages
were obtained ofthe eruptive staratthe U H 2.2m telescope through an R -band lter(5 m in
exposure)on Feb 1,2004 and through a narrow band H 2 2.12 m lter(20 m in exposure)on
Feb 14,2004 U T .
3. P re-outburst O bservations
O n January 23,2004,M cN eil(2004)2 discovered the presence ofa bright nebula m ore
than an arcm inute in extent south-west ofM 78 in the L1630 cloud,a nebula that was not
seen on any ofthe blue orred PO SS-I,PO SS-IIand U K ST U sky atlasplatestaken between
1951 and 1991. M cN eil’s N ebula is clearly com etary-shaped,w ith a highly reddened,dustobscured star at its apex. Subsequent exam ination of recent im ages obtained in the fall
of 2003 suggests that M cN eil’s N ebula rst appeared in late N ovem ber 2003 (Brice~
no et
al. 2004; M cN eil, priv. com m .). H owever, M r. John W elch of Phoenix, A rizona, kindly
brought our attention to a photograph ofthe M 78 region obtained by E.K reim er on O ct
22,1966 on w hich M cN eil’s N ebula is seen at virtually the sam e brightness as at discovery
(M allas& K reim er 1978).T his o ersthe im portantinsight thatthe current eruption ofthe
illum inating star is not the rst one. W e here sum m arize w hat is know n about this star
prior to the appearance ofthe nebula. T he star lies w ithin the error ellipse (4500 700 at PA
88o) ofthe IR A S source 05436{0007,w hich is detected only at 12 and 25 m w ith uxes of
0.53 and 1.19 Jy,respectively,w ith a ag that indicates an 80% probability that the uxes
are variable. T he star also coincides w ith the 2M A SS source 05461313{0006048,w hich is
located at 2000: 05h 46m 13.1s,and 2000: {00o0600500. T he 2M A SS photom etry is listed in
Table 1. A faint opticalcounterpart to this 2M A SS source is visible on an I-band im age
2
T his reference is listed as M cN eil, R eipurth, & M eech (2004) in the A strophysics D ata System . T he
second and third authorsonly provided a sim ple con rm atory C C D im age,and fullcreditforthe im portant
discovery ofthe eruption in IR A S 05436{0007 should go solely to M r. M cN eil. C onsequently,we suggest
that future reference to the discovery announcem ent in this IA U C ircular be given as M cN eil(2004).
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obtained by Eislo el& M undt (1997). In the sub-m illim eter, the source was detected as
a com pact,isolated dust continuum source at 350 and 1300 m by Lis,M enten, & Zylka
(1999),theirsource LM Z 12,a designation we w illuse forthe source in the follow ing untila
variable star nam e is assigned in the G C V S.Subsequently,the sam e source was detected at
850 m by M itchelletal.(2001)and Johnstone etal.(2001),theirsource O riBsm m 55.Lis
et al. (1999) suggested a pre-outburst bolom etric lum inosity for LM Z 12 of2.7 L . T hese
sub-m illim eterobservationsadditionally detected extended,di use em ission about40 arcsec
north ofLM Z 12,coinciding w ith partofM cN eil’s N ebula. Lim ited m illim eter observations
by Lis et al. (1999) did not revealany m olecular out ow from the source,and only a sm all
core in H C O + .
4. O bservational R esults
W e present in Fig.1 a color im age ofM cN eil’s N ebula based on g’,r’,and i’im ages
taken w ith G M O S at the G em ini-N telescope in 0.500 seeing. T he nebula has approxim ate
dim ensions of30 60 arcsec,and show s considerable structure,w ith a very bright patch
of illum ination near the source. Photom etry of LM Z 12 at its apex is given in Table 1.
N ote that because ofthe bright nebulosity,the stellar m agnitudes are very sensitive to the
aperture-size em ployed,we used a sm allaperture of0.900 radius.
T he nebula encom passes the H erbig-H aro object H H 22 (H erbig 1974). H owever, the
detection ofa collim ated jet associated w ith H H 22 em anating from a source further to the
East suggested to Eislo el& M undt (1997) that there is no connection between this H H
object and LM Z 12.A nother H H object,H H 23,islocated furtherto the N orth. Itconsists
oftwo knotson an axisthatpassesclose to LM Z 12,and Eislo el& M undt(1997)suggested
thatthe faintopticalsource coincident w ith LM Z 12 isthe driving source. M cN eil’s N ebula
opensup in the approxim ate direction towardsH H 23,and we suggestthatitrepresents the
illum inated out ow cavity carved atsom e tim e in the pastby LM Z 12 into the L1630 cloud.
Proper m otion m easurem ents ofH H 23 are needed to establish a rm er link w ith LM Z 12.
Infrared J,H ,K 0 photom etry ofthe source obtained on Feb 03,2004 islisted in Table 1.
Itisevidentthatthe source ism uch brighternow than w hen the 2M A SS data were obtained
on O ct 07, 1998. A t the tim e of our observations, LM Z 12 had brightened by J= 3.6,
H = 3.2,and K 0= 2.9 m agnitudes. W hen plotted in a J-H /H -K 0 diagram ,itisevidentthat
it displays a substantialinfrared excess (Fig.2). It is noteworthy that in its current high
state,LM Z 12 show sconsiderably lessreddening than atthe tim e ofthe 2M A SS observation
in 1998.
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In Fig.3 we show a contour diagram ofLM Z 12 as seen in our K 0-band im ages. It is
im m ediately obviousthatthe starissurrounded by a com pactre ection nebulosity and that,
in particular,this nebula show s a curved tailcharacteristic ofm any stars undergoing highaccretion events(e.g.,H erbig 1977).In Fig.4,weshow a K -band spectrum ofLM Z 12,w hich
displays a red continuum w ith strong C O -bandhead em ission,and the Br and N a I lines
are in em ission. O ur opticalspectrum ofLM Z 12 show s a red continuum w ith a prom inent
H line in em ission,but no other em ission or absorption lines,suggesting the presence of
heavy veiling. T he H line,show n in Fig.5,hasan equivalentw idth of 32 A and displaysa
characteristic P C ygnipro le. T he absorption com ponent has an equivalent w idth of5.6 A .
5. D iscussion
T hetwo m ajorclassesoferuptivevariablesam ong pre-m ain sequencestarsaretheFU ors
and the EX ors (H erbig 1966,1977,1989). In the follow ing we discuss w hether LM Z 12 can
be linked to one ofthese two categories.
FU orsarecharacterized by large-am plitude( V 5-6 m ag.) brighteningslasting several
or m any decades,and in the opticalthey show F-G type spectra w ithout em ission lines. In
the K -band region,FU ors display deep C O -bandhead absorption (e.g.,R eipurth & A spin
1997). A lthough LM Z 12 has about the right am plitude,it rem ains to be seen how long it
stays bright. Spectroscopically, however, LM Z 12 looks very di erent from m ature FU ors
both in the opticaland in the infrared. T he prom inent H em ission and the strong C O
em ission that are presently seen do not suggest a classi cation as a FU or as we currently
understand the phenom enon. O n the other hand,Brice~
no et al. (2004) em phasize that the
earliest optical spectrum after outburst of the FU or V 1057 C yg had som e sim ilarities to
that ofLM Z 12. Further photom etric and spectroscopic m onitoring ofthe star is required
to settle this.
EX or eruptions,w hich m ay occur repeatedly in a given star,have am plitudes that can
be com parable to those of FU ors, but they have durations w hich are m uch shorter, from
a few m onths to a few years. Spectroscopic studies of EX ors are lim ited, because of the
rarity and shorter durations ofthese eruptions. T he few such studies that have been m ade
(e.g., Lehm ann, R eipurth, & Brandner 1995; H erbig et al. 2001; Parsam ian et al. 2002)
allshow that EX ors in eruption have at least the lower Balm er lines in em ission,together
w ith em ission lines ofH e I and other lines characteristic ofthe m ost active T Tauristars
(H erbig 1962). A high-resolution spectrum ofthe H line ofSV S 13 in outburst (Eislo el
et al. 1991) show s a P C ygnipro le rather sim ilar to the one seen in Fig.5. H owever,we
do not see any other em ission lines than H in the spectralrange observed (4800-6800 A )
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in LM Z 12. Infrared spectra of EX ors are even m ore lim ited, one case is the eruption of
SV S 13,forw hich a K -band spectrum show s the C O bandheadsstrongly in em ission aswell
asBr in em ission (C arr& Tokunaga 1992).H owever,a sim ilarspectrum ofEX Lup show s
Br in em ission,butthe C O bandheadsand N a Iin absorption (H erbig etal.2001).Itthus
doesnotseem thatEX orshave a unique infrared spectralsignature. Based on a com parison
w ith these som ew hat lim ited observations ofEX ors,we conclude that LM Z 12 does have a
certain resem blance to EX ors.
T he spectroscopic data give us som e insight into the physicalprocesses behind the observed eruption. T he detection of Br in em ission testi es to a region of hot gas. Br
em ission has been show n to correlate tightly w ith accretion lum inosity,so its presence indicates thatthe eruption is linked to an episode ofaccretion (N ajita et al. 1996;M uzerolle et
al. 1998). T he pronounced P C ygnipro le seen at H in the opticalspectrum is likely to
be form ed in a strong w ind thathassu cient opticaldepth to produce the deep blueshifted
absorption trough (e.g., M uzerolle et al. 2001). O nly few T Tauristars show such welldeveloped P C ygni pro les at H . T he well-de ned blue edge of the absorption trough
indicates w ind velocities ofup to 600 km s 1,even m ore than the extrem e w ind that em anates from FU O rionis (e.g.,H erbig et al. 2003).
It is noteworthy that we see no spectral features indicative of shocks: the infrared
spectrum show s no evidence forH 2 em ission,and the opticalspectrum does not display the
[SII]6717/6731 lines characteristic ofH erbig-H aro jets. O ur H 2 2.122 m im age ofLM Z 12
show s no presence ofany extended jet ow . It thus appears that LM Z 12,in com m on w ith
m ost FU ors and EX ors,has powerfulm ass loss,but apparently not in the well-collim ated
fashion that enables shocked H H jets.
O ne nalinsight into the LM Z 12 EX or event com es from the changes ofthe infrared
colorsfrom beforeto aftertheeruption.T hepre-and post-outburstcolorsshow thatLM Z 12
hasm oved precisely along a reddening vector,indicating thatthe starhasbrightened partly
because its visual extinction dim inished by about 4.5 m agnitudes. U sing the reddening
curve of R ieke & Lebofsky (1985), we nd that this corresponds to A J = 1.26, A H = 0.81,
and A K = 0.50. Since we know that the infrared colors changed by J= 3.64, H = 3.16,
and K = 2.87,we see that the intrinsic brightening ofthe star corrected for the change in
extinction is 2.4 m agnitudes in each ofthe J,H ,and K lters. T hrough a com bination of
thisintrinsic brightening and the clearing away ofan obscuring layer,the starhasbeen able
to illum inate its out ow channel,thus creating M cN eil’s N ebula.
W e are gratefulto N uria C alvet for helpfulcom m ents, M ike C onnelley for taking an
infrared H 2 im age,G eorge H erbig for illum inating discussions,Inger Jorgensen and K athy
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R oth for a G M O S spectrum ,Jay M cN eilfor alerting us to the outburst,K aren M eech and
Yan Fernandez fora C C D im age,Peter M ichaud and K irk Pu’uohau-Pum m illforpreparing
the color-im age,Jean-R ene R oy for approving allthe G em ini8m ToO observations,Brian
Ski forinform ation aboutboth recentand pre-discovery im ages,John W elch forinform ation
about the 1966 outburst,and an anonym ous referee for helpfulcom m ents.
R E FE R E N C E S
Brice~
no,C .et al.2004,A pJ Letters,in prep.
C arr,J.S.,& Tokunaga,A .T .1992,A pJ,393,L67
C ohen,M .,K uhi,L.V .,H arlan,E.A .,Spinrad,H .1981,A pJ,245,920
Eislo el,J.,& M undt,R .1997,A J,114,280
Eislo el,J.et al.1991,A pJ,383,L19
H erbig,G .H .1962,A dv.A str.A strophys.,1,47
H erbig,G .H .1966, V istas in A stronom y,8,109
H erbig,G .H .1974,Lick O bs.Bull.N o.658
H erbig,G .H .1977,A pJ,217,693
H erbig,G .H .1989,in ESO W orkshop on Low M ass Star Form ation and Pre-M ain Sequence
O bjects,ed.B.R eipurth,p.233
H erbig,G .H .,A spin,C .,G ilm ore,A .C .,Im ho ,C .L.,Jones,A .F.2001,PA SP,113,1547
H erbig,G .H .,Petrov,P.P.,& D uem m ler,R .2003,A pJ,595,384
H ubble,E.P.1916,A pJ,44,190
Johnstone,D .,Fich,M .,M itchell,G .F.,M oriarty-Schieven,G .2001,A pJ,559,307
Lehm ann,T .,R eipurth,B.,Brandner,W .1995,A & A ,300,L9
Lis,D .C .,M enten,K .M .,& Zylka,R .1999,A pJ,527,856
M allas,J.H .,& K reim er,E.1978,T he M essier A lbum ,Sky Publishing C orporation
M cN eil,J.W .2004,IA U C 8284
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M itchell,G .F.,Johnstone,D .,M oriarty-Schieven,G .,Fich,M .,Tothill,N .F.H .2001,A pJ,
556,215
M uzerolle,J.,C alvet,N .,& H artm ann,L.1998,A J,116,2965
M uzerolle,J.,C alvet,N .,& H artm ann,L.2001,A pJ,550,944
N ajita,J.,C arr,J.S.,& Tokunaga,A .T .1996,A pJ,456,292
Parsam ian,E.S.,M ujica,R .,& C orral,L.2002,A strophysics,45,393
Pickering,E.C .1890,A nn.H arvard C ollege O bs.,18,113
R eipurth,B.,& A spin,C .1997,A J,114,2700
R eipurth,B.,& Bally,J.1986,N ature,320,336
R ieke,G .H .,& Lebofsky,M .J.1985,A pJ,288,618
Strom ,K .M .,& Strom ,S.E.1993,A pJ,412,L63
T his preprint was prepared w ith the A A S LATEX m acros v5.2.
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Table 1. Photom etry ofIR A S 05436{0007
D ate
O ct 7,1998
Feb 03,2004a
Feb 14,2004b
g’
r’
i’
J
H
K0
14.74 .03 12.16 .03 10.27 .02
11.1 .1
9.0 .1
7.4 .1
22.8 17.4 15.6
Telescope
2M A SS
G em ini
G em ini
a
W e listlarge and conservative errorestim atesforthe G em iniIR photom etry,since
this object is very bright for an 8m telescope,requiring very briefintegrations.
b
G M O S photom etry is obtained in an aperture w ith radius 0.900 in order to avoid
brightnearby nebulosity. Itisquoted to one decim alplace only since we use standard
zeropoints from the G em iniG M O S web site.
{ 10 {
Fig. 1.| A color-im age ofM cN eil’s N ebula obtained by com bining broadband g’,r’,and i’
im agesobtained w ith G M O S atthe G em ini-N 8m telescope. LM Z 12 isatthe bottom ofthe
nebula,and H H 22 isthe bluish curved objecton the northeastern edge ofM cN eil’s N ebula.
T he height ofthe gure is about 80 arcsec. N orth is up and East is left.
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Fig.2.| A J-H /H -K 0 diagram show ing the location ofLM Z 12 asobserved w ith 2M A SS [1]
on O ct7,1998 and w ith G em ini-N [2]on Feb 3,2004.T he dashed line isthe T Taurilocus,
and the solid straight lines and dot-dashed line are reddening vectors ofA V = 15 m ag.
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05:40
45
Declination (J2000)
50
55
−0:06:00
05
10
15
20
25
15.0
14.5
14.0
13.5
5:46:13.0
12.5
12.0
11.5
Right Ascension (J2000)
Fig. 3.| A com pact nebula is seen around the illum inating star ofM cN eil’s N ebula in this
K 0-band im age obtained w ith N IR Iat the G em ini-N 8m telescope.
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Fig.4.| A K -band spectrum ofLM Z 12 obtained w ith N IR Iatthe G em ini-N 8m telescope.
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Fig. 5.| T he H line in LM Z 12 show s a pronounced P C ygnipro le. T he rest velocity of
the star is indicated.