On the Progenitor of Supernova 2001du in NGC 1365

9 Pages·0.14 MB·

by  Schuyler D. Van Dyk

ToappearinPASP(2003April).
PreprinttypesetusingLATEXstyleemulateapj
ON THE PROGENITOR OF SUPERNOVA 2001DU IN NGC 13651
Schuyler D. Van Dyk
IPAC/Caltech, Mailcode100-22,PasadenaCA91125
Weidong Li and Alexei V. Filippenko
DepartmentofAstronomy,601CampbellHall,UniversityofCalifornia,Berkeley,CA94720-3411
To appear in PASP (2003 April).
ABSTRACT
Hubble Space Telescope (HST) WFPC2 archival images obtained years prior to the explosion of the
3
0 Type II-plateau supernova (SN) 2001du in NGC 1365 previously have been analyzed to isolate the
0 progenitor star. The SN site was located using precise astrometry applied to the HST images, with
2 significant uncertainty, leaving three possible progenitor candidates. Images of the fading SN have
recently become publicly available in the HST archive, allowing us to pinpoint the SN’s exact location
n
on the pre-explosion images. We show that the SN occurred in very close proximity to one of the blue
a
J candidatestars,butwearguethatthisstarisnottheactualprogenitor. Instead,the progenitorwasnot
4 detected on the pre-SN images, and we constrain the progenitor’s mass to be less than 13+−74 M⊙. This
2 is consistent with previous constraints on the progenitor masses of other Type II-plateau supernovae
(SNe), suggesting that such SNe arise from the iron core collapse of massive stars at the lower extreme

2 of the possible mass range.
v
Subject headings: supernovae: general—supernovae: individual(SN2001du)—stars: massive—stars:
6
evolution — stars: variables: other — galaxies: individual (NGC 1365)
4
3
1 1. INTRODUCTION 2. ANALYSIS
0
Supernova 2001du was visually discovered by R. Evans Pre-SN images, each of total exposure time 300 s in
3
(2001) on August 24.7 (UT dates are used throughout the bands F336W,F555W,andF814W,were obtainedby
0
/ this paper) at the western end of the bar in the spiral GTO-5222on1995January15. Late-time multi-bandim-
h galaxyNGC1365(about90′′Wand10′′Softhenucleus). agesoftheSNwereobtainedbyGO-9041on2001Novem-
p
Smartt, Kilkenny, & Meikle (2001) classified the SN as ber 26. These include deep images in F336W, F439W,
-
o Type II; Wang et al. (2001), from a spectrum obtained F555W,F675W,andF814W,aswellasshorterexposures
r on August 30 UT, confirmed the SN as Type II-plateau in F336W, F555W, and F814W. The available HST data
t
s (II-P) before optical maximum. NGC 1365 has also been aresummarizedinTable1,withtotalexposuretimesgiven
a host to SN 1957C (of unknown type) and the Type Ic SN for each band.
v: 1983V.UsingHubbleSpaceTelescope (HST)observations In Van Dyk et al. (2003) we adopted the position of
i of Cepheids, Silbermann et al. (1999) determined the dis- theSN,measuredfromanimageobtainedwiththeYALO
X tance modulus of NGC 1365 to be µ = 31.3±0.2 mag, 1-m telescope at CTIO (and available on the Internet),
r corresponding to a distance of about 18.2 Mpc. as α = 3h33m29s.15, δ = −36◦08′31′.′5 (J2000), with to-
a Van Dyk, Li, & Filippenko (2003) recently measured tal uncertainty ±0′.′9. The SN site is located on the WF3
the absolutepositionofSN2001duand,applyinganinde- chip. In Figure 1 we reproduce Figure 21 from Van Dyk
pendentastrometricgridtopre-SNHST archivalWFPC2 et al., showing the SN environment in the F555W band.
images, isolated three possible candidate progenitor stars In Figure 2 we show the late-time F555W image (the SN
within the uncertainty of the measured SN position: one is nearly centered on the PC chip for all the GO-9041 ex-
reddish star with a detection in both the F555W and posures). As one cansee, the actualSN position is within
F814Wbands,andtwostarswithonlyF555Wdetections, the 0′.′9 error circle, which provides additional confidence
implying bluer colors for these latter two stars. Also, in the astrometric method used by Van Dyk et al. when
multi-band WFPC2 images of the SN were obtained for isolating the various SN sites2.
HST program GO-9041 (PI: S. Smartt) in 2001 Novem- We initially used the routine HSTphot (Dolphin
ber. These images are now in the public domain, and 2000a,b) to obtain photometry of the objects imaged
in this paper we analyze them and compare them to the on the PC chip. HSTphot automatically accounts
pre-SN images to further constrain the nature of the SN for WFPC2 point-spread function (PSF) variations and
progenitor. (Smarttetal.2003havealsorecentlyanalyzed charge-transfer effects across the chips, zeropoints, aper-
their images and, in a somewhat similar manner, come to ture corrections, etc., and can return as output magni-
the same basic conclusion that we reach here.)
1BASED ON OBSERVATIONS MADE WITH THE NASA/ESA HUBBLE SPACE TELESCOPE, OBTAINED FROM THE DATA
ARCHIVEOFTHESPACETELESCOPESCIENCEINSTITUTE,WHICHISOPERATEDBYTHEASSOCIATIONOFUNIVERSITIES
FORRESEARCHINASTRONOMY,INC.,UNDERNASACONTRACTNAS5-26555.
2ApplyingthesameastrometricmethodusedbyVanDyketal.(2003) tothemosaicofthedeepF555W exposure,wemeasureaposition
forSN2001dutobeα=3h33m29s.14,δ =−36◦08′31′.′3(J2000), ±0′.′2ineachcoordinate.
1
2
tudes transformed from the HST flight system to stan- In Van Dyk et al. (2003) we had isolated three faint
dard Johnson-Cousins bands. Van Dyk et al. (2003) dis- objects, A–C, detected and determined to be stellar by
cussthesimilarityintheresultsfromHSTphot,compared HSTphot, within the error circle around the SN position.
withthosefromthepackagesDoPHOT(Schechter,Mateo, Stars A and B, to the south and west, respectively, are
& Saha 1993) and DAOPHOT/ALLSTAR (Stetson 1987, both blue, with m (∼V) = 24.30±0.21 mag and
F555W
1992).3 25.02±0.32mag,respectively,andnodetectionsatF814W
The SN profile is saturated in the longer F555W (V), (∼I). (Blue, here, is relative, and includes stars with
F675W (R), and F814W (I) exposures. Thus, no bright- roughly early-G spectral type or earlier, based on the de-
ness measurement is possible. The SN is not saturated tectionlimits; see below.) Star C,to the east, is relatively
in the shorter F555W and F814W exposures, the long red, with V = 24.44±0.23 and V −I = 1.03±0.30 mag.
F336W(U)andF439W(B)exposures,andalsothe short We had assumed that, since SN 2001du is of Type II-P,
F336W exposure. However, the results from HSTphot for the most plausible of the three candidates is the redder
the F336W exposures varied, depending on how these ex- star. However, that was argued to be still unlikely, based
posureswerecombinedwiththe other bandsas inputinto on the assumed luminosity and color of Star C.
the routine, andthe resultsfromthe long andshortexpo- Wehaveusedthelate-timeSNimages,specificallytheV
sures for this band were also discrepant with each other image, and attempted to match them up with the pre-SN
(theresultsrangedfromaboutm =18.9to18.7mag images. This was done by using the task geotran in IRAF
F336W
for different runs of HSTphot). We do not know why this to transform both the late-time SN images to the pre-SN
occurred, but we speculate that it possibly may be due to imagesandviceversa. Wecanthereforelocatetheposition
the low signal-to-noise ratio for both exposure sets. For of the SN on the pre-SN images as being 0.70±0.15 WF
F336W we then applied to both the long and short expo- pixel (0′.′07) northeast of the position of Star B. It would
suresDAOPHOT/ALLSTARwithinIRAF4asacheck,us- be tempting to assign Star B, then, as the progenitor of
ingaTinyTimPSF(Krist1995),thezeropointfromHoltz- SN 2001du. However, (1) the offset of the SN position
man et al. (1995), and aperture corrections (∼0.00 mag) from Star B (which corresponds spatially to 6.2 pc at the
derived from artificial star tests. (Checks for the F439W distanceofNGC1365)issignificantlylarge,andtheaccu-
andshortF555WandF814WexposureswithDAOPHOT racyofthe measurementis appreciablyhigh; (2)SNe II-P
show good agreement with the HSTphot results.) arethoughttoarisefromtheexplosionsofredsupergiants;
Weobtainedm =18.96±0.10and18.87±0.04mag and (3) no evidence exists that SN 2001du is peculiar in
F336W
fortheshortandlongexposures,respectively. Wethenav- any way and that it arose from a bluer, more compact
eraged these DAOPHOT magnitudes with the HSTphot starliketheprogenitorofSN1987A(E.Cappellaro,2002,
magnitudes at F336W, and obtained m = 18.86 private communication). Thus, it is more likely, as we
F336W
mag. The SN was quite red by late November 2001, with previously had suspected (Van Dyk et al. 2003), that the
m −m =1.82 mag. Whether using the trans- progenitor simply is not detected in the pre-SN images.
F336W F439W
formations from flight system to Johnson-Cousins magni- We canuse the detectionlimits ofboth the F555Wand
tudes from Holtzman et al. (1995), Dolphin (2000b), or F814W pre-SN images to constrain the nature of the pro-
via SYNPHOT applied to the Bruzual Spectral Synthetic genitor. We do this by inferring limits on the luminosity
Atlas (see Van Dyk, Filippenko, & Li 2002), this color is and, therefore, the mass from the limits on the star’s ap-
too red to obtain a reliable transformation from m parentmagnitude. These HSTphotdetectionlimits inthe
F336W
toU. However,wedoapplyatransformation,withuncer- SNenvironmentarem >25.19andm >24.25
F555W F814W
tainty ∼0.2 mag. The transformations for all other bands mag. Beforeconvertingintoabsolute magnitude, wemust
are from Dolphin (2000b), applied internally within HST- firstassesstheamountofextinctiontotheSN.InVanDyk
phot. The final results for the photometry of SN 2001du etal.(2003)weattemptedtousestarsintheenvironment
in the HST images are presented in Table 2. to estimate the reddening. The Galactic extinction to-
InFigure3weshowpreliminary,unpublishedBVI light ward NGC 1365 is AV = 0.07 mag (Schlegel, Finkbeiner,
curves for SN 2001du, based on data from the YALO 1- & Davis 1998; and NED5). We had found that stars in
m telescope (N. Suntzeff & K. Krisciunas, 2003, private the larger SN environment implied larger amounts of ex-
communication), and we include the UBVI photometry tinction, AV ≈ 2.5 mag. (Unfortunately, although the
from the HST data. For comparison we show the B and post-SN images are deeper than the pre-SN ones, the SN
V light curves for the plateau-type SN (II-P) 1999em in is far too bright, and its image is spread over too many
NGC1637(Leonardetal.2002a). Itisclearlyevidentthat surrounding pixels, to perform a more thorough study of
SN 2001du is indeed a SN II-P as well. If this SN were a the environment.)
linear-type event (II-L), it should have markedly declined Using the light curve in Figure 3 we canactually derive
in brightness by the time of the HST observations (∼94 morespecificinformationaboutthepossiblereddeningto-
days since discovery). wardthe SN fromthe SNitself (whichis informationthat
wasnotavailabletous previously). TheHST photometry
of the SN on November 26 is about 94 days after discov-
3. DISCUSSION ery, i.e., near the end of the light-curve plateau, where we
3In fact, here we update the private communication by D. C. Leonard 2002, regarding the very good agreement between the results of
HSTphot photometry onimages of NGC 3351, compared withthose obtained by Graham etal. (1997) usingDAOPHOT;Leonard now finds
δV =0.015±0.022andδI =0.036±0.018mag.
4IRAF(ImageReductionandAnalysisFacility)isdistributedbytheNationalOpticalAstronomyObservatories,whichareoperatedbythe
AssociationofUniversitiesforResearchinAstronomy,Inc.,undercooperativeagreement withtheNationalScienceFoundation.
5NEDistheNASA/IPACExtragalacticDatabase, http://nedwww.ipac.caltech.edu.
3
can still estimate the SN’s colortemperature with reason- are roughly consistent with what we showed in Figure 22
able accuracy (e.g., Hamuy et al. 2001). These colors are of Van Dyk et al. (2003). We therefore estimate that the
B−V =1.42andV −I =0.91mag. Forcomparison,the uppermasslimitfortheSN2001duprogenitoris13+−74M⊙.
colorsoftheverywell-studiedTypeII-PSN1999ematthe This limit is consistent with the limit Leonard et
asanmdeVag−eI(ab=ou0t.8995mdaaygs(aLfteeorndarisdcoevterayl.)2a0re02Ba)−.VLe=on1a.4rd7 ∼al.1(720M02⊙b)limfinitdofnoer fiSnNdsIIf-oPr S1N999IgI-iP(1159+−9539eMm,⊙i)fathneddthise-
et al. and Hamuy et al. (2001) conclude that SN 1999em tancetotheSN1999emhostisassumedtobetheCepheid
is reddened by E(B −V) = 0.10 mag. Since B − V is distance,11.5±0.9Mpc(Leonardetal. 2003). Lowmasses
affected by line blanketing in the B band (e.g., Hamuy et for the progenitors of SNe II-P, relative to that indicated
al.2001),thesmalldifferenceinB−V (SN1999emis0.05 for SNe II-L (linear) and SNe IIn (narrow), are also in-
magredderthanSN2001du)couldbeduetodifferencesin ferred from their optical properties (e.g., Schlegel 1996;
metallicity between the two SNe, which might affect this Filippenko 1997; Chugai & Utrobin 2000) and suggested
color. The marginally redder V −I color of SN 2001du by the inferred paucity of circumstellar matter from radio
(by 0.02 mag) may imply that this SN is slightly more and X-ray observations (e.g., Weiler et al. 1989; Schlegel
reddened than SN 1999em. However, we consider these 2001; Pooley et al. 2002).
differences in color between the two SNe to be small and
likely within the uncertainties in the colors, so we adopt 4. CONCLUSIONS
E(B − V) ≈ 0.1 mag for SN 2001du, as found for SN Comparing HST archival WFPC2 images obtained of
1999em. the Type II-P SN 2001duin NGC 1365at late times with
If we assume the Cardelli, Clayton, & Mathis (1989) imagesobtainedbefore explosion,we havelocatedthe po-
reddening law, then AV ≈ 0.3 mag and AI ≈ 0.2 mag sitionofthe SN progenitorstar to within 1 WF chippixel
for SN 2001du. For the distance modulus µ = 31.3 mag, ofthecandidateStarBidentifiedbyVanDyketal.(2003).
MV > −6.4 and MI > −7.0 mag for the progenitor star. This star, however, is more than likely not the progeni-
In a similar vein to the estimation of the progenitor mass tor. Weusethedetectionlimitsofthepre-SNF555Wand
limit for SN II-P 1999em by Smartt et al. (2002) and SN F814Wimagestoplaceconstraintsontheprogenitor’sna-
II-P 1999gi by Smartt et al. (2001), the absolute magni- ture; specifically, M ∼<13+−74 M⊙. (Smartt et al. 2003 find
tudelimitscanbeconvertedtotheluminosityofthelikely
a similar mass limit of M = 15 M⊙.) This limit is con-
supergiant progenitor, assuming the full range of possible
sistent with what has been found and inferred for other
stellar surface temperatures. This is accomplished using
SNe II-P.
a similar relation to equation (1) in Smartt et al. (2001,
Theproximityofthe SNtotheblue StarBimpliesthat
2002), where we also have assumed the temperatures and
theprogenitormayhavebeenpartofasmallstellarassoci-
stellarbolometriccorrectionsforsupergiantsfromDrilling
ation(theseparationbetweentheprogenitorandStarBis
& Landolt (2000) and have computed, using SYNPHOT
likelytoolargeforthebluestartobeabinarycompanion).
within IRAF and the Bruzual Spectral Atlas, the conver-
The faint emission underlying Stars A, B, and C identi-
sions of m and m to Johnson V for the range
F555W F814W fied by Van Dyk et al. (2003)suggests that an association
in spectral type. The luminosity limits for both F555W
complexmaylieintheSNenvironment. Itwouldbeinter-
(V) and F814W (I) are shown in Figure 4. Stars with lu-
esting to image the SN againin multiple bands with HST
minosities brighter than these limits (shown by the heavy
at high spatial resolution, presumably with the Advanced
lines) should have been detected in the pre-SN images.
Camerafor Surveys (ACS), when the SN has significantly
Forcomparisonwehaveplotted(alsoinasimilarfashion
dimmed. The stars in the environment of the fading SN
to Smartt et al.) the model stellar evolutionarytracks for
would then become more obvious, and the age and mass
arangeofmassesfromLejeune&Schaerer(2001),assum-
ofthe progenitorstar mightbe further constrained,based
ingenhancedmasslossforthemostmassivestarsandthat
on the characteristics of its surviving neighbors.
a metallicity Z = 0.04 is appropriate for the SN environ-
ment. Indication for a metallicity somewhat greater than
This research made use of the NASA/IPAC Extra-
solarinthissectorofNGC1365comesfromtheabundance
galactic Database (NED) which is operated by the Jet
studybyRoy&Walsh(1997)ofHIIregionsinthegalaxy.
Propulsion Laboratory, California Institute of Technol-
The closest H II regions to the SN site are their Nos. 20
ogy, under contract with NASA, and the LEDA database
and 21, where at this radial distance from the nucleus,
the O/H abundance is ∼9 dex or, in fact, slightly greater, (http://leda.univ-lyon.fr). The work of A.V.F.’s group
at UC Berkeley is supported by NASA grants AR-8754,
based onmodel assumptions (the solarO/Habundance is
AR-9529, and GO-8602 from the Space Telescope Sci-
8.8 dex; Grevesse & Sauval 1998).
ence Institute, which is operated by AURA, Inc., under
TheluminositylimitsateachbandinFigure4showthat
NASAcontractNAS5-26555. WethankD.C.Leonardand
thepre-SNimagesarenotsensitivetothebluesthigh-mass
M. Hamuy for useful discussions. We also thank the ref-
supergiants, so we cannot be absolutely sure that such a
eree, K. Krisciunas, for helpful comments and for provid-
star is not the progenitor. If we exclude this possibility,
ing unpublished ground-based photometry of SN 2001du.
the V band sets an upper limit to the progenitor mass
of ∼ 13 M⊙, although this ranges upward to as high as
∼ 20 M⊙, depending on the effective temperature. The
I band is more sensitive to less-massive red supergiants,
ranging downward to ∼ 9 M⊙ (possibly even less) at the
lowesteffective temperatures. TheseresultsfromFigure4
4
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Table 1
Summary of HST Observations
Date Filter Exp. Time HST SN
(UT) (s) Program Saturated?
1995 Jan 15 F336W 300a GTO-5222 ···
F555W 300 ···
F814W 300 ···
2001 Nov 26 F336W 100 GO-9041 N
460 N
F439W 400 N
F555W 40 N
600 Y
F675W 400 Y
F814W 40 N
600 Y
aThe exposure times for all three bands in this 1995 Jan 15 dataset were erroneously listed in Van Dyk et al. (2003)
as 100 s. The actual total exposure time of 300 s results from the combination of a trio of 100-s exposures. Note that
HSTphot automatically reads the correct total exposure time from the images during processing, so the reported results
are unaffected by this error.
5
Table 2
Photometry of the SN 2001du HST Images
U B V R I
[m ] [m ] [m ] [m ] [m ]
F336W F439W F555W F675W F814W
18.6(0.2)a 16.72(0.06) 15.30(0.00) ··· 14.39(0.00)
[18.86]b [17.04] [15.32] ··· [14.43]
aThe value in parentheses for each entry in this row is the uncertainty in the transformed Johnson-Cousins
magnitude.
bThe value in brackets for each entry in this row is the adopted flight-system magnitude, derived from
HSTphot, DAOPHOT, or both.
Fig. 1.— The site of SN 2001du in the archival 300-s F555W image from 1995 January 15. The error circle has radius
0′.′9. The three stars, A–C, within the circle are indicated with tickmarks. This is a reproduction of Fig. 21 from Van
Dyk et al. (2003).
Fig. 2.—SN 2001du,asseeninthe 600-sF555Wimagefrom2001November26,showntothe samescaleandorientation
as in Figure 1. The error circle from Figure 1 is also shown. The supernova is saturated in this image.
6
Fig. 3.— The light curves of SN 2001du. The open pentagons, open squares, and open triangles are BVI measurements
from images obtained using the YALO 1-m telescope (N. Suntzeff & K. Krisciunas, 2003, private communication). The
filled symbols are the measurements from the HST images. Also shown for comparisonare the measurements in B (five-
pointed stars) and V (four-pointed stars) for the Type II-P SN 1999emfrom Leonard et al. (2002a),adjusted by ∼1 mag
to match the V peak for SN 2001du.
7
Fig. 4.—Hertzsprung-Russelldiagramshowingmodelstellarevolutionarytracks(alternatinglong-dashed lines andshort-
dashed lines) for a range of masses from Lejeune & Schaerer (2001), with enhanced mass loss for the most massive stars
and a metallicity Z =0.04. Also shownare the luminosity limits (heavy solid lines) for both the F555W (V) and F814W
(I) bands. Stars with luminosities brighter than these limits should have been detected in the pre-SN HST images.
This figure "fg1.jpg" is available in "jpg"(cid:10) format from:
http://arXiv.org/ps/astro-ph/0301346v2
This figure "fg2.jpg" is available in "jpg"(cid:10) format from:
http://arXiv.org/ps/astro-ph/0301346v2