The $^{7}$Be II Resonance Lines in Two Classical Novae V5668 Sgr and V2944 Oph

2.1 MB·

by  Akito Tajitsu

Draftversion January21,2016
PreprinttypesetusingLATEXstyleemulateapjv.5/2/11
THE 7Beii RESONANCE LINES IN TWO CLASSICAL NOVAE V5668 SGR AND V2944 OPH
Akito Tajitsu1, Kozo Sadakane2, Hiroyuki Naito3, Akira Arai4, Hideyo Kawakita4, and Wako Aoki5
Draft version January 21, 2016
ABSTRACT
We reportspectroscopicobservationsof the resonancelines ofsingly ionized7Be in the blue-shifted
absorption line systems found in the post-outburst spectra of two classical novae – V5668 Sgr (Nova
6
1 Sagittarii 2015 No.2) and V2944 Oph (Nova Ophiuchi 2015). The unstable isotope, 7Be, should has
0 been createdduring the thermonuclear runaway(TNR) of these novae and decays to form 7Li within
2 a short period (a half-life of 53.22 days). Confirmations of 7Be are the second and the third ones
following the first case found in V339 Del by Tajitsu et al. (2015). The blue-shifted absorption line
n
a systems in both novae are clearly divided into two velocity components, both of which contain 7Be.
J This means that the absorbing gases in both velocity components consist of products of TNR. We
0 estimate amounts of 7Be produced during outbursts of both novae and conclude that significant 7Li
2 should have been created. These findings strongly suggest that the explosive production of 7Li via
the reaction 3He(α,γ)7Be and subsequent decay to 7Li occurs frequently among classical novae and

] contributes to the process of the Galactic Li enrichment.
R
Subject headings: stars: individual(V5668 Sgr, V2944 Oph); (stars:) novae, cataclysmic variables –
S nucleosynthesis, abundances; Galaxy: evolution – abundances
.
h
p
1. INTRODUCTION The produced 7Be will be blown away from the surface
-
o Lithium(Li)isakeyelementinthestudyofthechem- of a WD by the outburst wind, then decays to form 7Li
r inthecoolerinterstellarenvironmentwithinashorttime
ical evolution of the universe because it likely has been
st produced in various sites and events – Big Bang nucle- (a half-life of 53.22 days). In the 1990s, details of this
a process, which is called as the Cameron-Fowler process,
osynthesis, interactions between energetic cosmic rays
[ were studied by theoretical analyses (Boffin et al. 1993;
and interstellar matter, evolved low-mass stars, novae,
Hernanz et al. 1996; Jos´e & Hernanz 1998).
1 and supernova explosions. The observed Li evolution-
v ary curve has a plateau for young Galactic ages (< 2.5 Recently, we have reported the detection of 7Be in
8 Gyr) followedby a steep rise. This indicates that a rela- the post-outburst UV spectra of the classical nova V339
6 tivelylow-massstellarcomponentwithlonglifetimesisa Del (Tajitsu et al. 2015). Because the resonance dou-
1 major sourceof Li in the recent universe (Romano et al. blet lines of Beii are located at ∼3130 ˚A where the
5 1999,2001;Prantzos2012). Somelow-massevolvedstars telluric absorption mainly caused by ozone severely ob-
0 haveindeedbeenfoundtohaveLi-enrichedsurfaces(e.g., structsobservationsfromground-basedtelescopes,quan-
1. Melo et al. 2005). However, there has been no observa- titative studies of the stellar Be abundances have been
0 tional confirmation that such stars supply Li to inter- enabled in 1990s by the advent of 8-10 m class tele-
6 stellar medium. Li contained in stellar surface could scopesonhighmountains. Theyareequippedwithhigh-
1 easily be depleted by convection, because Li should be resolution spectrographs having high sensitivities in the
: destroyed inside stars where temperature is higher than near-UV region [e.g., Boesgaardet al. 1999 (Kecki tele-
v
2.5 million K. scope); Primas et al. 2000 (VLT)]. Extensive analyses
i
X Novae, which evolve from low-mass binaries, are ex- of stellar Be abundances were conducted for large sam-
pected to be one of the candidates for Li suppliers ples of metal-poor stars (Boesgaardet al. 2011) and so-
r
a in the recent universe, because they experience ex- laranalogs(Takeda et al.2011). InthecaseofV339Del,
plosive nucleosynthesis and mass-loss simultaneously. we found that the absorption lines of Beii were purely
Cameron & Fowler (1971) made the first theoretical originating from 7Be instead of the stable 9Be. There-
studyofLiproductioninnovae. Theypredictedthatthe fore, it was the first observational confirmation of the
radioactive isotope of beryllium, 7Be, produced via the Cameron-Fowlerprocessinclassicalnovae. The 7Be was
reaction 3He(α, γ)7Be during the TNR in the accumu- foundinhighlyblue-shifted(radialvelocities,vrad∼1000
latedthingaslayeronthesurfaceofawhitedwarf(WD). kms−1) absorption lines, which are assumed to corre-
spondto novaejecta blownofffromthe surfaceofaWD
[email protected] by the outburst wind. Through the direct comparison
1Subaru Telescope, National Astronomical Observatory of ofabsorptionstrengthsbetween7BeiiandCaii,weesti-
Ja2paAns,tr6o5n0oNmoicrtahl AIn’sothitouktue,PlOacsea,kaHilKo,yoHikIu96U72n0i,veUrsSiAty, Asahi- matedthatthe 7Beabundance inthe ejecta ofV339Del
could be higher than the pre-existing theoretical predic-
gaoka, Kashiwara,Osaka582-8582, Japan
3Nayoro Observatory, 157-1 Nisshin, Nayoro, Hokkaido 096- tion (Jos´e & Hernanz 1998). Izzo et al. (2015) reported
0066, Japan the presence of the Liiλ6708 line in the blue-shifted ab-
4Koyama Astronomical Observatory, Kyoto Sangyo Univer-
sorption line system in the early phase (7–13 days af-
sity,Motoyama,Kamigamo,Kita-ku,Kyoto603-8555, Japan
5NationalAstronomicalObservatoryofJapan,2-21-1Osawa, ter the outburst) spectra of V1369 Cen (Nova Centauri
Mitaka,Tokyo181-8588,Japan 2013). The overabundanceof Li inthis nova amounts to
2 Tajitsu et al.
the order of 104 with respect to the solar photospheric
composition.
Nowitisquiteinterestingtoknowhowcommonlythis
7Be (=7Li) production occurs among various types of
classical novae and evaluate their contribution to the Li
evolution in the Galaxy. Prompted by these interests,
we have performed high resolution spectroscopic obser-
vations of two Galactic novae discovered in March 2015
– V5668 Sgr and V2944 Oph, during their early decline
phases.
V5668 Sgr (Nova Sagittarii 2015 No.2 = PNV
J18365700−2855420) was discovered as a bright 6.0
magnitude (unfiltered) source by John Seach on 2015
March 15.634 UT and announced in the American As-
sociation of Variable Star Observers (AAVSO) Alert
Notice (Waagen 2015a). The nova recorded its op-
tical maximum (V = 4.3) on March 21.67 UT
(MJD=57102.67). Its optical magnitudes stayed close
to the maximum (V ∼ 4.5 – 6.5) for about 80
days, then showed a rapid decline by dust formation
(Banerjee et al. 2015a,b; Gehrz et al. 2015). The pos-
sible candidates of the progenitor were found in the
′′
USNO-B1.0 catalogue (Monet et al. 2003) within 6
from the nova (USNO-B1.0 0610-078494.3, B1=17.17,
R1=16.82, R2=16.42, I=15.55mag; USNO-B1.0 0610-
0784923, R1=14.36, B2=13.62, R2=13.65, I=15.08
mag), and in the Galaxy Evolution Explorer (GALEX;
Martin et al. 2005) catalogue of NUV (1171–2831 ˚A)
′′
sources 3 .6 from the nova (GALEX J183656.8-285539,
NUV=17.323 mag) (Waagen 2015a). From a spectro-
scopic observation obtained immediately after the dis-
covery,Williams et al. (2015) reported that it is an Feii
type nova according to the classification introduced by
Williams (1992).
V2944 Oph (Nova Ophiuchi 2015 = PNV
J17291350−1846120) was discovered as a 12.2 mag-
nitude (unfiltered) source by Yukio Sakurai on 2015
Fig.1.— The light curves of V5668 Sgr (a) and V2944 Oph
March 29.766 UT (Waagen 2015b). After its discovery,
(b) observed in Visual, B, V, and R bands by the AAVSO team.
the nova showed a gradual rise to its optical maximum Thedifferentbandsareplottedindifferentcolorsandsymbols(see
at V = 9.0 on April 14.75 UT (MJD = 57126.75). legends in the figure). The epochs of our HDS observations are
Then, it showed a quick decline to V ∼ 11.5 within indicatedbyarrows.
the following few days, and stayed at V ∼ 12 for > 80
days. In the USNO-B1.0 catalogue, a possible candi- 2. OBSERVATIONS
date of the progenitor was found as a ∼18 magnitude
The post-outburst spectra of the two classical novae
star at the position of the nova (Waagen 2015b). Its
were obtained using the High Dispersion Spectrograph
spectrum during the pre-maximum phase showed He/N
(HDS) (Noguchi et al. 2002) of the 8.2-m Subaru Tele-
type characteristics (Danilet et al. 2015). However,
scope on 2015May 29 (V5668 Sgr; +69 d after the opti-
Munari et al. (2015) concluded that it is an Feii type
cal maximum) and July 3 (V2944 Oph; +80 d), respec-
nova by spectroscopic observations carried out during
tively. Figure1 shows the AAVSO light curves of two
themaximumandearlydeclinephase. Munari & Walter
novae with the epochs of our HDS observations. In the
(2016) presented observations of the time evolution in
case of V5668 Sgr, our observation was just before the
lineprofilesduringthepre-maximumphase,andpointed
start of the rapid decline in optical magnitudes by dust
out the presence of pre-existing circumstellar materials
formation. For each nova, we obtained spectra under 3
around the nova. They concluded that the companion
configurationsofthespectrograph,whichcoverthewave-
in the nova system is not a main sequence dwarf as in
most novae but an evolved sub-giant. length regions from 3030 to 4630 ˚A, from 4110 to 6860
In this paper, we report the detection of strong 7Be ˚A, and from 6670 to 9360 ˚A. Spectral resolving power
absorption lines in these two novae. In Section 2, we was set to R ≃ 60000 and 45000 with 0′′.6 (0.3 mm)
′′
describe our high resolution spectroscopic observations and 0 .8 (0.4 mm) slit widths, respectively. The details
anddataanalysis. Theresultsfromourobservationsare of observations are reported in Table 1. Data reduction
described in Section 3. The 7Be abundances estimated was carried out using the IRAF software in a standard
from our observed data are presented in Section 4. A manner. Thenon-linearityinthedetectorsarecorrected
brief discussion and conclusions are given in Section 5. by the method described in Tajitsu et al. (2010). The
typical residual of wavelength calibration performed us-
7Be in V5668 Sgr and V2933 Oph 3
TABLE 1
Journalof HDSobservations oftwo novae
Date UTa MJD Exposure Range Resolution
2015 (hm) (s) (˚A)
V5668Sgr
May29 1043 57,171.447 600 4110-6860 60,000
(+69d)b 1203 57,171.502 3,600 3030-4630 60,000
1357 57,171.581 300 6670-9360 60,000
V2944Oph
Jul03 655 57,206.289 900 6670-9360 45,000
(+80d)c 710 57,206.299 900 4110-6860 45,000
744 57,206.322 5,400 3030-4630 45,000
aUTistheuniversaltimeatthestartofanexposure.
bDaysaftertheoptical (V)maximum(MJD=57,102.67).
cDaysaftertheoptical (V)maximum(MJD=57,126.75).
ing Th-Ar comparison spectrum is smaller than 10−3 ˚A
for each spectrograph configuration. Spectrophotomet-
ric calibration was performed using the spectrum of σ
Sgr (V = 2.058, B2V) obtained nearly at the same alti-
tude of the nova on the same nights. All spectra were
converted to the heliocentric scale. Correction for inter- Fig. 2.—ExamplesectionsofthefluxcalibratedHDSspectrum
of V5668 Sgr obtained at +69 d. Theenlarged views of the spec-
stellar extinction has not been applied. The line identi-
trum in the hatched areas are presented in Figure4. Identified
fications werecarriedoutusing the atomic line database absorption linesystems originating from Fe-peak elements arein-
of Kramida et al. (2014). We also used the line list of dicatedbyticksatthetop.
Kurucz & Bell (1995) for some weak transitions of Fe-
peak elements.
3. RESULTS
The post-outburst spectra of V5668 Sgr (+69 d) and
V2944Oph(+80d), whicharedisplayedinFigure2and
Figure3, respectively, show very similar spectral char-
acteristics. They contain a series of strong broad emis-
sion lines originating from Hi Balmer series and some
other permitted transitions originating from Feii. As in
the case of V339 Del described in Tajitsu et al. (2015),
most of these broad emission lines are accompanied by
blue-shifted multiple absorption lines, whose radial ve-
locities correspond to ∼ −2000 – −800 kms−1. Many
blue-shifted absorption lines of Tiii, Crii, and Feii are
found in the near UV region.
Figure4 displays the enlarged views of the spec-
trum of V5668 Sgr in the vicinities of the Hγ, CaiiK,
7Beiiλ3131.228,NaiD , Feii(the multiplet number 42;
2
Moore 1959)λ5169.03, and Lii lines, on the velocity
scale. The blue-shifted absorption lines of the Hγ line
is clearly found to be divided into two components; the
low velocity component (LVC) is a single sharp absorp-
tion line at a relatively low v ∼−786 kms−1, and the Fig. 3.—ExamplesectionsofthefluxcalibratedHDSspectrum
rad
highvelocitycomponent (HVC) containsa seriesofsub- ofV2944Ophobtainedat+80d. Theenlargedviewsofthespec-
components spreading between −2200 < v < −1350 truminthehatched areasarepresentedinFigure5.
rad
kms−1. The radial velocities of each sub-component are
measuredat the absorptiondips in the Feii(42)and Hγ HVC vary among different transitions. All of six sub-
line, and indicated with vertical lines in the figure. The components in the HVC can be identified in the Hγ and
sharp absorption of the LVC can be easily identified in Feii(42)lines,althoughsomeofthemareweakerormiss-
all lines in the figure. These LVC lines originating from ing in Caii and Nai lines. In the UV range, only the
singly ionized Fe-peak elements (Feii, Tiii, Crii, Mnii, sub-components at v = −1385 and −1444 kms−1 of
rad
and Niii) dominate the spectrum in the UV range as in the HVC canbe identified inthe stronglines originating
the case of V339 Del from +38 to +48 d. All of the from Fe-peak elements.
identified transitions originate from levels of low exci- Figure5 presents the spectrum of V2944 Oph dis-
tation potentials (the lower energy level of the transi- played in the same way as in Figure.4. The spectrum
tion, E . 3.1 eV). The absorption strengths of the of this nova shows quite similar characteristics to that
lower
4 Tajitsu et al.
Fig.4.— The blue-shifted absorption line systems in the spec- Fig.5.—Sameas Figure4,but forthespectrum of V2944Oph
trum of V5668 Sgr. The spectrum obtained at +69 d is dis- obtainedat+80d. Thespectrumissmoothedbya3pixelboxcar.
played in the vicinities of Hγ, CaiiK, 7Beiiλ3131.228, NaiD2, Cosmic-rayhits onthespectrum inthe vicinityof 7Beii areindi-
Feii(42)λ5169.03,and7Liiλ6707.76lines(toptobottom),onthe catedwithcrosses. Inthebottompanel,therearenocounterparts
velocity scale (upper horizontal). The local continua, fitted with ofthe7LiidoubletortheCai(32)lines.
high-order (15–25) spline functions, are over-plotted with thick
lines (orange in the online version). Dips of individual absorp-
tionline,whichcanbeidentifiedinFeiiand/or Hγ,areindicated of V5668 Sgr. It also shows the blue-shifted absorption
with vertical lines (green in the online version). The identified systems divided into two velocity components; the LVC
dips by the other component of the doublet are also indicated in at v = −878 kms−1 and the HVC between −2000 <
tphaerts7BofeitiheanbdlueN-sahiiDftepdaanbeslso.rptIinonthlienebosyttsotemmspaonfetlh,en7oLiciouonrttehre- vradr<ad−1300 kms−1. At least six sub-components can
Cai(32)λ6717.69 lines are found in their expected wavelengths beidentifiedintheHVCasshownbyverticallinesinthe
(solidanddashedverticallines). figure.
7Be in V5668 Sgr and V2933 Oph 5
Fig.6.— Enlargedradial velocity profiles of the LVC and the redsideedge of the HVC inV5668 Sgr (upper) and V2944 Oph(lower).
NormalizedspectrainthevicinitiesofFeii(42)λ5169,Hγ,andthe7Beiidoubletaredisplayedwithoffsets. Thesolidverticallinesindicate
absorption components identified in the 7Beii doublet and other lines. The dashed vertical lines show absorption components identified
onlyinFeiiand/orBalmerlines. Theexpected positionsofthe9Beiidoubletareindicatedbypartialdashedlines. IntheLVCinV2944
Oph(lower-bottompanel),thespectruminthevicinityof7Beiilinesissmoothedbya3pixelboxcar,andasub-componentatvrad=−849
kms−1 isfoundineachline(thedipA+;theorangeverticallineintheonlineversion).
As shown in the bottom panels of Figure 4 and 5, we component of the doublet) in the LVC in this nova is
cannot find any counterparts of blue-shifted absorption unclear due to the poor signal-to-noise ratio, which is
line systemsofthe 7Liiλ6708inspite ofthe highsignal- partly disturbed by cosmic ray hits on the spectrum. A
to-noise ratios of the spectra (∼ 700 and ∼ 160 at 6690 sub-component in the LVC at v = −849 kms−1 (the
rad
˚A in V5668 Sgr and V2944 Oph, respectively). There dip A+) is found in the Feii and both 7Beii lines. We
is also no counterpart of the Cai(32)λ6718 in the spec- can find no alternative candidates of identifications for
tra of both novae, although this line has been detected these dips from line lists of Fe-peak elements. Because
together with the Liiλ6708 line in the first three weeks no dips corresponding to the 9Beii doublet [the isotopic
spectra of V1369 Cen (Izzo et al. 2015). The Caiλ4227 shift;∆λ=−0.161˚A(Yan et al.2008)]canbefound,we
and Kiλ7699 lines do not have any counterparts in the conclude that the absorption systems at ∼ 3110 – 3125
LVC and the HVC in both observed novae. These ob- ˚A in both novae are purely originating from 7Beii as in
servations imply that the ejected gas had been heated the case of V339 Del. The dips of the 7Beii doublet be-
into so hot state that almost all Li and Ca atoms are comehardtobeidentifiedtowardtheflatbottomsofthe
ionized in the circumstance during epochs of our HDS HVC in both novae. This indicates that the absorption
observations. of7Beiiissaturated,whiletheintensitiesattheflatbot-
Figure6 displays the enlarged radial velocity profiles tomsremain∼25and∼15%ofthecontinuainV5668Sgr
of Feii, Hγ, and the 7Beii “doublet” lines in both no- andV2944Oph,respectively. InV5668Sgr,theHVCsof
vae. Although the 7Beiiλλ3130.583,3131.228 doublet the Balmer lines show wavy bottom shapes. This differ-
lines are coalesced each other, the dips of each line can enceindicatesthatthe7Beiiabsorptionisstrongerthan
bepartiallyidentified. InV5668Sgr,twoabsorptiondips the Balmer lines at this velocity range.
(A and B) are clearly found in all lines. In V2944 Oph, Itisinterestingtoseethesimilarityinthevelocitypro-
two dips (B and C) of the 7Beii doublet coincide with filesoftheblue-shiftedabsorptionsystemsinbothnovae.
those of Hγ. The dip A of 7Beiiλ3131.228 (the weaker Someofclassicalnovaealsohavesimilarblue-shiftedab-
6 Tajitsu et al.
sorption systems with two distinct velocity components of the absorbing gas cloud to the background illuminat-
– the narrow LVC and the broad HVC (e.g., Nova LMC ing source has no wavelength dependence. We notice
2005, V2574 Oph in Williams et al. 2008), which are that the LVC feature of 7Beii at −786 kms−1 of V5668
knownasthe“principal”andthe“diffuseenhanced”sys- Sgr might be saturated. The bottom of the 7Beii lines
tems in post-maximum nova spectra (McLaughlin 1960; in the LVC almost reaches to that in the HVC, where
Munari 2014). V1369 Cen at +13 d also has two ve- its flat profile suggests that the absorption is saturated.
locity components at v = −550 and −1300 < v The correspondingLVC componentofthe CaiiK line in
rad rad
< −900 (Izzo et al. 2015). One remarkable point found V5668 Sgr is shallow and the line appears to be unsat-
inthisstudyisthat7BeisdetectedinboththeLVCand urated. The abundance of 7Be in V5668 Sgr obtained
the HVC. This means that both of the absorption sys- under such a condition should be taken as a lower limit.
temsconsistofnovaejectawhichhaveexperiencedTNR. Following Spitzer (1998, Equation (3)-(48)), the ratio
Thecharacteristicsofthe LVCsinV5668SgrandV2944 of column number densities, N, can be written as
Oph closely coincide with those of the Transient Heavy
N(7Beii) W(7Beii) λ(CaiiK)2
Element Absorption (THEA) found by Williams et al. = × ×
(2008) in post-outburst spectra of classical novae. They N(Caii) λ(7Beii)2 W(CaiiK)
assumedthattheseTHEAsareproducedbypre-outburst gf(CaiiK)
ejecta coming from the secondary star. Considering our
gf(7Beiiλ3130.583)+gf(7Beiiλ3131.228)
resultsonthe7Be detection,however,itis naturaltoas-
sumethattheTHEAsareproducedbynovaejectawhich =W(7Beii) × 39342
have experienced TNR. 31312 W(CaiiK)
The 7Beii absorption may be contaminated by LVCs 10+0.135
originating from other Fe-peak elements. We set re- × . (1)
quirements for major contaminants as E < 3.1 eV 10−0.178+10−0.479
lower
and log(gf) > −1.0, and select candidates for contam- Usingdataofthe W(7Beii)andthe W(CaiiK)listedin
inants as listed in Table2. Only some Crii(5) lines are
Table3, the column density ratios, N(7Beii)/N(Caii),
found to be the main contaminants to the LVC and the
derived in the LVC of V5668 Sgr and V2944 Oph are
HVC of the 7Beii doublet. In V5668 Sgr, the dip of the 8.1±2.0 and 2.5 ±1.5, respectively. These ratios are
Crii(5)λ3132.053 is clearly identified within the 7Beii
close to that found in V339 Del at +47 d.
LVC (Fig.6 upper-right panel). In the 7Beii HVC, no
The ionization states of each species are keys to con-
Crii(5) lines canbe identified because ofthe strongsat-
vert the above ratios into atomic abundances. We as-
urationeffect. However,theirequivalentwidths(W)can sume that the most of 7Be is in the singly ionized state,
beestimatedusingmeasuredequivalentwidthsofnearby
because it still stays in hot ejecta. We also assume that
unblended Crii lines belonging to the same multiplets.
Ca is in the singly ionized state. The absence of Cai
We estimate that the combined contributions of these
linesintheblue-shiftedabsorptionlinesystemssupports
contaminants are less than 5% of the total equivalent
this assumption. The difference in the second ioniza-
widths of the 7Beii absorptionin both the LVC and the
tion potential (Be: 18.21 eV, Ca: 11.87 eV) may lead
HVC in V5668 Sgr. In the case of V2944 Oph, we find
to different balances between the second and the third
that only the Crii(5)λ3132.053 is present besides the
ionized ions and this may be a source of an error in de-
LVC of the 7Beii doublet. We estimate that the com-
termining the abundances. We tried but failed to de-
bined contribution of contaminants in the HVC in this
tect absorption lines of doubly ionized ions of Fe-peak
nova is similar to or less than that in V5668 Sgr.
elements, which have intermediate second ionization po-
tentials, consulting Kramida et al. (2014). Absorption
4. 7Be ABUNDANCE lines of Feiii are observed in optical range spectra of B-
Weplaced“best-effort”localcontinuaaroundeachline type stars (Thompson et al. 2008). This may support
(−3000 < v < 1000 kms−1) on the complex, undu- the assumption that all of 7Be and Ca contained in the
rad
lating spectra of two novae by the fitting with a high- LVC are in the singly ionized state. Adopting this as-
order (15 – 25) spline function to measure the equiva- sumption,themassfractionof7Betothesumofallcon-
lent widths of the absorption lines. Although the 7Beii stituent mass components, X(7Beii), can be presented
doublet cannot be resolved, its total equivalent widths, as: X(7Be) ∼ N(7Beii)/N(Caii)×7/40×X(Ca). We
W(7Beii)s,intheLVCandtheHVCaremeasured. After have obtained X(7Be)/X(Ca)=1.4±0.3 for V5668 Sgr
subtracting the combined effects of contaminations dis- and 0.44±0.26 for V2944 Oph. These X(7Be)/X(Ca)
cussedabove,we tabulate the resulting W(7Beii) in Ta- valuescorrespondtologarithmicoverabundancesofLiby
ble3. The errors of W are estimated from the signal-to- +6.2 dex and +5.7 dex with respect to the solar photo-
noise ratios of the neighboring-continuum. They do not spheric abundance (Asplund et al. 2009). As in the case
include the uncertainties in the continuum placements. of V339 Del, the Li abundances in ejecta of both nova
The abundances of 7Be in nova ejecta is estimated explosions are comparable to or even higher than those
following the same procedure as used in Tajitsu et al. of Ca. Because the results presented here are based on
(2015). We compare the equivalent widths of CaiiK the observations ∼ 75 – 100 days after their outbursts,
(log(gf) = +0.135) and 7Beiiλ3130.583 + λ3131.228 the amount of 7Be freshly produced in the TNR could
(log(gf) = −0.178,−0.479, respectively) in the LVC, be 3 – 4 times larger than our measurements.
which show a simpler structure than the HVC. Here, We note that these abundances are obtained only us-
we need the following assumptions; (1) both the 7Beii ingalimitedfractionofthenovaejectagivingrisetothe
and Caii lines are not saturated, (2) the covering factor LVC absorption. They do not necessarily represent the
7Be in V5668 Sgr and V2933 Oph 7
TABLE 2
Lines originatingfromFe-peakelements in the vicinity of the 7Beiidoublet
V5668Sgr V2944Oph
Lines λlab log(gf) λLVCa 7Beiib W (˚A)c λLVCa 7Beiib W (˚A)c
Tiii(67) 3106.246 −0.170 3098.11 — <0.003 3097.16 — <0.006
Tiii(67) 3117.676 −0.500 (3109.51) HVC — (3109.51) HVC —
Crii(5) 3118.646 0.000 (3110.48) HVC (0.054±0.026) (3109.52) HVC (0.037±0.020)
Tiii(67) 3119.825 −0.460 (3111.65) HVC — (3110.69) HVC —
Crii(5) 3120.359 +0.120 (3112.18) HVC (0.071±0.034) (3111.23) HVC (0.049±0.030)
Crii(5) 3120.497 −0.018 (3112.32) HVC (0.052±0.025) (3111.36) HVC (0.036±0.020)
Crii(5) 3128.692 −0.320 3120.49 — 0.013±0.003 3120.49 — <0.006
Crii(5) 3132.053 +0.079 3123.85 LVC 0.067±0.015 3123.85 — 0.045±0.015
Crii(5) 3136.681 −0.250 3128.46 — 0.045±0.015 3128.46 — <0.006
aTheobservedandexpectedwavelengthsoftheLVCs(vrad =−786and−878kms−1inV5668SgrandV2944Oph,respectively)ofeach
transition. Theundetected linesinthe7BeiiHVCarelistedinbrackets.
bThevelocitycomponent ofthe7Beiidoubletexpected tobecontaminated bytheline.
cTheobservedorexpected equivalent widthsofeachline. Thevaluesestimatedusingnearbysamemultipletsarelistedinbrackets.
TABLE 3
Equivalentwidths of blue-shiftedabsorption lines in observednovae
HVC LVC
W(7Beii) W(7Beii) W(CaiiK) N(7Beii) X(7Be)
Object Day
(˚A) (˚A) (˚A) N(Caii) X(Ca)
V5668Sgr +69d 6.40±0.98 1.30±0.22 0.35±0.02 8.1±2.0 1.4±0.30
V2944Oph +80d 3.64±0.30 0.20±0.10 0.18±0.03 2.5±1.5 0.44±0.26
V339Del +47d
−1103 kms−1 0.16±0.010 0.089±0.003 3.9±0.4 0.68±0.07
−1268 kms−1 0.064±0.015 0.023±0.004 6.5±2.5 1.1±0.44
abundances in the whole materials erupted from these 5. DISCUSSION AND CONCLUSIONS
novae. Furthermore,when the 7Beii lines are saturated, The detection of 7Be in the post-outburst spectra of
the above X(7Be)/X(Ca) values shouldbe treated care-
V5668 Sgr and V2944 Oph strongly suggests that the
fully. Therefore, the derived 7Be abundances in this explosive production of 7Be is a popular phenomenon
study might involve large uncertainties. However, the among classical novae. The light curves of both novae
aboveresultimplies thatclassicalnovaeareindeedplay- showslowerevolutionthanthatofV339Delinwhichthe
ing an important role in the process of the Galactic Li rapid decline were observed in ∼ +40 d. Adopting the
enrichment. relationbetweenthetime-scalingfactorofthelightcurve
To produce 7Be via the reaction 3He(α, γ)7Be, the andtheWDmass(e.g.,Hachisu & Kato2006,2015),the
total number of 3He atoms in the accreted gas before WD masses of both novae are lower than that of V339
TNR should be larger than or equal to that of freshly Del. It is natural to assume that both novae have CO
produced 7Be atoms in nova ejecta. This means that WDs as in the case of V339 Del. Therefore, we infer
thenumberratios,N(3He)/N(Ca),intheaccretedgases thattheexplosiveLiproductionviatheCameron-Fowler
of V5668 Sgr and V2944 Oph are & 8.1 ± 2.0 and process occurs frequently at least among CO novae.
&2.5±1.5,respectively. Ifweadoptthesolarabundance It is interesting to notice that we havefound LVC and
ratio between He and Ca (log(N(He)/N(Ca)) = +4.59; HVC absorptions of the NaiD lines in V5668 Sgr and
Asplund et al. 2009), the lower limits of the number ra- V2944Oph,while notraceofblue-shiftedabsorptionsof
tios between 3He and 4He, N(3He)/N(4He), in the ac- theNaiDlinesweredetectedinV339Del(Tajitsu et al.
cretedgasesofV5668SgrandV2944Ophshouldamount 2015). We find no absorption features corresponding
to 0.020±0.005and0.006±0.003%,respectively. These to Liiλ6708, Kiλ7699, and Caiλ4227 in both V5668
isotopic ratios are close to that found in the solar sys- Sgr and V2944 Oph as well as in V339 Del. Izzo et al.
tem (= 0.0166%; Asplund et al. 2009). Hernanz et al. (2015) found blue-shifted absorptions of Hβ and NaiD
(1996) pointed outthat 3He destructionviathe reaction lines in V1369 Cen at two velocities (−1100 and −550
3He(3He, 2p)4He occurs concurrentlywith 3He(α, γ)7Be kms−1) on spectra obtained during early phase after
during TNR. They noted that the 3He destruction via the outburst (7 to 13 days). They identified Liiλ6708,
3He(3He,2p)4He is lesspronouncedinCOnovaethanin Kiλ7699, Caiλ6718 and Caiλ4227 in the lower veloc-
ONenovae. BecausebothV5668SgrandV2944Ophare itycomponent. Theseapparentspectraldifferences,such
found to be CO novae (see the next section), we guess as detection or no-detection of absorptions of the NaiD
that the process of 3He destruction should be ineffective or Cai lines, should reflect differences in physical con-
and that most of 3He in the accreted gases have been ditions (most probably the ionization state) in the ab-
converted into 7Be in both novae. sorbing clouds. On the other hand, the presence of 7Be
8 Tajitsu et al.
bothintheLVCandtheHVCstronglyindicatesthatthe of novae including both 7Be and Li lines and examine
absorbing clouds in both velocity components consist of the consistency of derived Li abundances. Further ob-
materials which have experienced TNR. servations of the 7Beii line in various types of classical
The abundance of Li obtained by Izzo et al. (2015) novae will help to quantify roles of novae as the source
from the Liiλ6708 is lower than the 7Be (= Li) abun- of Li in the current universe.
dances obtained in the present study. There had been
no report in literature of detection of the Liiλ6708 line
amongpost-outburstnovaebeforeIzzo et al.(2015). Be- This work is based on data observed at the Subaru
causethe Liiλ6708islocatedinthe easilyaccessiblered Telescope, which is operated by the National Astronom-
spectralregion,the paucity of observationalinformation icalObservatoryofJapan(NAOJ).Weacknowledgewith
mayimply thatejecta ofpost-outburstnovaerarelyper- thanks the variable star observations from the AAVSO
mits the physical condition in which neutral Li can sur- International Database contributed by observers world-
vive. However, it will be interesting to carry out long wide and used in this research.
term monitoring observations of post-outburst spectra Facilities: Subaru(HDS).
REFERENCES
Asplund,M.,Grevesse,N.,Sauval,A.J.,&Scott, P.2009, Monet,D.G.,Levine,S.E.,Canzian,B.,etal.2003,AJ,125,984
ARA&A,47,481 Moore,C.E.1959,AMultipletTableofAstrophysicalInterest:
Banerjee,D.P.K.,Ashok,N.M.,&Srivastava,M.2015a,The NBSTechnicalNoteNo.36,ReprintedVersionofthe1945
Astronomer’sTelegram,7299,1 edition(USDepartmentofCommerce)
Banerjee,D.P.K.,Ashok,N.M.,Venkataraman, V.,& Munari,U.2014,inAstronomicalSocietyofthePacific
Srivastava, M.2015b, TheAstronomer’sTelegram,7303, 1 ConferenceSeries,Vol.490,StellaNovae:PastandFuture
Boesgaard,A.M.,Deliyannis,C.P.,King,J.R.,etal.1999,AJ, Decades, ed.P.A.Woudt &V.A.R.M.Ribeiro,183
117,1549 Munari,U.,Ochner,P.,Siviero,A.,Dallaporta,S.,&Valisa,P.
Boesgaard,A.M.,Rich,J.A.,Levesque, E.M.,&Bowler,B.P. 2015,TheAstronomer’sTelegram,7367,1
2011, ApJ,743,140 Munari,U.,&Walter,F.M.2016,MNRAS,455,L57
Boffin,H.M.J.,Paulus,G.,Arnould,M.,&Mowlavi,N.1993, Noguchi,K.,Aoki,W.,Kawanomoto, S.,etal.2002,PASJ,54,
A&A,279,173 855
Cameron,A.G.W.,&Fowler,W.A.1971,ApJ,164,111 Prantzos,N.2012,A&A,542,A67
Danilet,A.B.,Holoien,T.W.-S.,Wagner,R.M.,etal.2015, Primas,F.,Molaro,P.,Bonifacio,P.,&Hill,V.2000, A&A,362,
TheAstronomer’sTelegram,7339,1 666
Gehrz,R.D.,Evans,A.,Woodward,C.E.,etal.2015, The Romano,D.,Matteucci, F.,Molaro,P.,&Bonifacio,P.1999,
Astronomer’sTelegram,7862,1 A&A,352,117
Hachisu,I.,&Kato,M.2006,ApJS,167,59 Romano,D.,Matteucci, F.,Ventura,P.,&D’Antona,F.2001,
—.2015,ApJ,798,76 A&A,374,646
Hernanz,M.,Jose,J.,Coc,A.,&Isern,J.1996, ApJ,465,L27 Spitzer,L.1998,PhysicalProcessesintheInterstellarMedium
Izzo,L.,DellaValle,M.,Mason,E.,etal.2015,ApJ,808,L14 Tajitsu,A.,Aoki,W.,Kawanomoto,S.,&Narita,N.2010,Publ.
Jos´e,J.,&Hernanz,M.1998,ApJ,494,680 Natl.Astron.Obs.Japan,13,1
Kramida,A.,Yu.Ralchenko,Reader,J.,&andNISTASDTeam. Tajitsu,A.,Sadakane, K.,Naito,H.,Arai,A.,&Aoki,W.2015,
2014, NISTAtomicSpectraDatabase (ver.5.2),[Online]. Nature,518,381
Available:http://physics.nist.gov/asd [2015,July23]. Takeda,Y.,Tajitsu,A.,Honda,S.,etal.2011,PASJ,63,697
NationalInstitute ofStandards andTechnology, Gaithersburg, Thompson,H.M.A.,Keenan,F.P.,Dufton,P.L.,etal.2008,
MD. MNRAS,383,729
Kurucz,R.,&Bell,B.1995,AtomicLineData(R.L.Kuruczand Waagen, E.O.2015a,AAVSOAlertNotice,512
B.Bell)KuruczCD-ROMNo.23.Cambridge,Mass.: —.2015b, AAVSOAlertNotice,516
SmithsonianAstrophysicalObservatory, 1995.,23 Williams,R.,Mason,E.,DellaValle,M.,&Ederoclite,A.2008,
Martin,D.C.,Fanson,J.,Schiminovich,D.,etal.2005, ApJ, ApJ,685,451
619,L1 Williams,R.E.1992,AJ,104,725
McLaughlin,D.B.1960, inStellarAtmospheres,ed.J.L. Williams,S.C.,Darnley,M.J.,&Bode,M.F.2015,The
Greenstein(TheUniversityofChicagoPress),585–652 Astronomer’sTelegram,7230,1
Melo,C.H.F.,deLaverny,P.,Santos,N.C.,etal.2005,A&A, Yan,Z.-C.,N¨ortersha¨user,W.,&Drake,G.W.F.2008,Physical
439,227 ReviewLetters,100,243002