[show abstract][hide abstract] ABSTRACT: We examine the ejecta evolution of the classical nova V1065 Centauri, constructing a detailed picture of the system based on spectrophotometric observations obtained from 9 to approximately 900 days post-outburst with extensive coverage from optical to mid-infrared wavelengths. We estimate a reddening toward the system of E(B-V) = 0.5 ± 0.1, based upon the B – V color and analysis of the Balmer decrement, and derive a distance estimate of 8.7+2.8 –2.1 kpc. The optical spectral evolution is classified as P o fe N ne A o according to the CTIO Nova Classification system of Williams et al. Photoionization modeling yields absolute abundance values by number, relative to solar of He/H = 1.6 ± 0.3, N/H = 144 ± 34, O/H = 58 ± 18, and Ne/H = 316 ± 58 for the ejecta. We derive an ejected gas mass of Mg = (1.6 ± 0.2) × 10–4 M ☉. The infrared excess at late epochs in the evolution of the nova arises from dust condensed in the ejecta composed primarily of silicate grains. We estimate a total dust mass, Md , of order (0.2-3.7) × 10–7 M ☉, inferred from modeling the spectral energy distribution observed with the Spitzer IRS and Gemini-South GNIRS spectrometers. Based on the speed class, neon abundance, and the predominance of silicate dust, we classify V1065 Cen as an ONe-type classical nova.
The Astronomical Journal 10/2010; 140(5):1347. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: Nova V2362 Cygni has undergone a number of very unusual changes. Ground-based spectroscopy initially revealed a normal sequence of events: the object faded and its near-infrared emission lines gradually shifted to higher excitation conditions until about day 100 when the optical fading reversed and the object slowly brightened. This was accompanied by a rise in the Swift X-ray telescope flux and a sudden shift in excitation of the visible and IR spectrum back to low levels. The new lower excitation spectrum revealed broad line widths and many P-Cygni profiles, all indicative of the ejection of a second shell. Eventually, dust formed, the X-ray brightness—apparently unaffected by dust formation—peaked and then declined, and the object faded at all wavelengths. The Spitzer dust spectra revealed a number of solid-state emission features that, at this time, are not identified.
The Astronomical Journal 09/2008; 136(5):1815. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: CCD UBVRi photometry of the final helium flash object V4334 Sgr (Sakurai's object) carried out during 1997–1999 is presented, and the light curve from its prediscovery rise to the dust obscuration phase is constructed. The optical light curve can be divided into four sections, the rise to maximum, the maximum, the dust onset, and the massive dust shell phase. The color indices show a general increase with time, first because of the photospheric expansion and cooling and later because of the dust-forming events. The energy distributions for the years 1996–1999 show that an increasing part of the energy is radiated at infrared wavelengths. In 1996 the infrared excess is likely caused by free-free radiation in the stellar wind. Starting from 1997 or 1998 at the latest, carbon dust grains are responsible for the more and more dramatic decrease of optical radiation and the growing infrared excess. Its photometric behavior in 1998–1999 mimics the "red declines" of R CrB variables; the amplitude, however, is more extreme than any fading ever observed in an R CrB star. Evidence is given that a complete dust shell has formed around V4334 Sgr. It therefore shows similarities with dust-forming classical novae, although it is evolving ~20 times more slowly. Its luminosity increased by a factor 4 between 1996 and 1998. A comparison of timescales of the final helium flash objects FG Sge, V605 Aql, and V4334 Sgr shows that the observed photometric and spectroscopic features are similar, while V4334 Sgr is the most rapidly evolving object to date.
The Astronomical Journal 12/2007; 119(5):2360. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: A J A c c e p t e d 2 0 0 7 A J A c c e p t e d 2 0 0 7 – 2 – ABSTRACT We report optical photometry and optical through mid-infrared spectroscopy of the classical nova V1186 Sco. This slowly developing nova had an complex light curve with multiple secondary peaks similar to those seen in PW Vul. The time to decline 2 magnitudes, t 2 , was 20 days but the erratic nature of the light curve makes determination of intrinsic properties based on the decline time (e.g., luminosity) problematic, and the often cited MMRD relationship of della Valle & Livio (1995) fails to yield a plausible distance. Spectra covering 0.35 to 35 µm were obtained in two separate epochs during the first year of out-burst. The first set of spectra, taken about 2 months after visible maximum, are typical of a CO-type nova with narrow line emission from H I, Fe II, O I and He I. Later data, obtained between 260 and 380 days after maximum, reveal an emerg-ing nebular spectrum. Spitzer spectra show weakening hydrogen recombination emission with the emergence of [Ne II] (12.81 µm) as the strongest line. Strong emission from [Ne III] (15.56 µm) is also detected. Photoionization models with low effective temperature sources and only marginal neon enhancement (Ne ∼ 1.3 Ne ⊙) are consistent with these IR fine-structure neon lines indicating that V1186 Sco did not occur on a ONeMg white dwarf. In contrast, the slow and erratic light curve evolution, spectral development, and photoionization analysis of the ejecta imply the outburst occurred on a low mass CO white dwarf. We note that this is the first time strong [Ne II] lines have been detected so early in the outburst of a CO nova and suggests that the presence of mid-infrared neon lines is not directly indicative of a ONeMg nova event. Subject headings: stars: individual (V1186 Sco) — stars: novae.
The Astronomical Journal 04/2007; 10181818(3). · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: Aims.We present optical and near-infrared spectral evolution of the Galactic nova V5114 Sgr (2004) during few months after the outburst.
Methods: .We use multi-band photometry and line intensities derived from spectroscopy to put constrains on the distance and the physical conditions of the ejecta of V5114 Sgr.
Results: .The nova showed a fast decline (t$_2$ sime 11 days) and spectral features of Fe II spectroscopic class. It reached M$_V$ = -8.7 plusmn 0.2 mag at maximum light, from which we derive a distance of 7700 plusmn 700 kpc and a distance from the galactic plane of about 800 pc. Hydrogen and oxygen mass of the ejecta are measured from emission lines, leading to ~10$^-6$ and 10$^-7$~M_sun, respectively. We compute the filling factor of the ejecta to be in the range 0.1-10$^-3$. We found the value of the filling factor to decrease with time. The same is also observed in other novae, then giving support to the idea that nova shells are not homogeneously filled in, rather being the material clumped in relatively higher density blobs less affected by the general expanding motion of the ejecta.
[show abstract][hide abstract] ABSTRACT: If two novae, one fast and one slow, were to go off simultaneously in a distant galaxy, the fast one would be the brighter of the two. But this means that at some point in time after peak brightness, the two novae, fading at different rates, would become equal in brightness. From a study of recent novae in the Large Magellanic Cloud (LMC), we find that 13 days is, on the average, that interval of time, and the average absolute magnitude then is MV = -6.32 ± 0.17. This result is markedly different from that obtained for galactic novae.
The Journal of the American Association of Variable Star Observers. 01/2005; 33(2):207-211.
[show abstract][hide abstract] ABSTRACT: Classical nova (CN) explosions are thermonuclear runaway (TNR) in the
accreted H-rich envelope on the white dwarf (WD) in a cataclysmic
variable system. Infrared and optical observations of CN have
established their importance for understanding the formation of
astrophysical grains, and as contributors to abundance anomalies in the
ISM on local scales. Abundance studies of nova ejecta also provide
information about nucleosynthesis in the WD progenitor and in the TNR.
Here, we present Spitzer Space Telescope IRS spectra of the Galactic
Classical nova V1187 Scorpii (Nova Scorpii 2004 #2) as well as
coordinated optical spectroscopy and photometry obtained on the MMT
6.5-m and the 2.0-m robotic Liverpool telescopes.
The Spitzer spectra, obtained on 28.40 September 2004 UT as part of our
Cycle 1 ToO nova program, exhibit broad ( ˜ 4800 km/s)
H-recombination line emission (e.g., HI 6-5, HI 7-6, HI 9-8) as well as
forbidden line emission including [Mg VII]5.50 micron, [Mg V]5.61
micron, [Ne II]12.81 micron, and [Ne III]15.55 micron. Of note, the [O
IV]25.89 micron line is present in the spectra of V1187 Sco. The high
resolution optical spectra, obtained on 2004 September 23.01 UT, show
double peaked emission lines with velocity components separated by
˜ 1200 km/s, suggesting that the ejecta of V1187 Sco is
distributed in clumps of varying ionization states exhibiting a range of
ejection velocities (frequently found in CN). We present a preliminary
discussion of line identification, reddening, abundances, as well as a
comparison of V1187 Sco to other ONeMg nova. Our Spitzer observations
are also supported by complementary ground-based infrared spectra obtain
as part of a large collaborative study of this nova (see posters by
Lynch et al. and Russell et al.).
This work is supported in part by NASA (JPL/SSC) and the NSF
[show abstract][hide abstract] ABSTRACT: Stars are the engines of energy production and chemical evolution in our
Universe. They deposit radiative and mechanical energy into their
environments, and enrich the ambient interstellar medium with elements
synthesized in their interiors and dust grains condensed in their
atmospheres. Classical novae (CN), a transient phenomenon, contribute to
this cycle of chemical enrichment through explosive nucleosynthesis and
the violent ejection of material dredged from the white dwarf progenitor
and mixed with the accreted surface layers. Using Spitzer (+IRS), we
propose a 10.5 hr, no-impact, multi-cycle (2) ToO program to study (in
temporal detail) the later evolutionary stages of CN (> 40 days
post-outburst) by targeting 4 Galactic and 3 Magellanic Cloud novae.
Spitzer is a unique facility that can enable us to investigate aspects
of CN phenomenon including: the in situ formation and astromineralogy of
dust, the elemental abundances resulting from thermonuclear runaway, the
correllation of ejecta masses with progenitor type, the bolometric
luminosities of the outburst, and the kinematics and structure of the
ejected envelopes. Specifically, our program addresses four research
problems in the study of CN evolution: 1)~determination of the grain
size distribution and mineral composition of nova dust; 2)~estimation of
chemical abundances of nova ejecta from coronal and forbidden emission
line spectroscopy; 3)~measurement of the density and masses of the
ejecta; and 4)~characterization of the nature of novae in the SMC and
LMC at mid- to far-infrared wavelengths.
[show abstract][hide abstract] ABSTRACT: Some 34 novae have been discovered in the LMC and 14 in the SMC. Historically, the novae seemed to avoid the central bar of the LMC and the main body of the SMC, but with the novae discovered in the past two decades a different picture emerges. The more dramatic situation exists in the SMC where all seven of the most recent novae have occurred in or very near the main body. Indications are that the age f the LMC bar is around 5 Gyr (Smecker-Hane et al. 2002), certainly old enough to breed novae. Perhaps the puzzle now is why there have been so many novae in the disk component of the LMC where many H II regions are found.
Variable Stars in the Local Group, IAU Colloquium 193; 01/2004
[show abstract][hide abstract] ABSTRACT: Studying classical novae in the Magellanic Clouds has at least three huge advantages: (1) their distances are well-known; (2) the interstellar extinction is small and reasonably well known; and (3) an abundance of novae (47 as of 2003 September 15) have been discovered in the two clouds. Consequently, we will investigate in this paper one of the most important characteristics of novae: the relationship between the absolute magnitudes of the nova outbursts at maximum brightness and their rate of decline, often referred to as the MMRD.
Variable Stars in the Local Group, IAU Colloquium 193; 01/2004
[show abstract][hide abstract] ABSTRACT: UBV and BVR photometry of $\eta$ Car during the 2003.5 low-excitation event – the considered periastron passage of a binary – is presented. The light and colour curves show a number of features, which were also seen at previous periastron passages: a light maximum of long duration with a superimposed flare-like event which is temporarily interrupted by an eclipse-like dip, and a steep decline in the $U-B$ color index. The $R$ brightness reached a minimum at the time of mid X-ray totality, probably implying that the H$\alpha$ emission line reached a minimum. The source of the optical flare-like event is probably not the same as the one causing the the X-ray radiation. It is tempting to consider the epoch of the $R$ minimum and the mid- X ray totality – which roughly coincides with the UBV minimum – as the central moment of the 2003.5 low-excitation event.
[show abstract][hide abstract] ABSTRACT: Six-color broadband photometry of Sakurai's Object, a star that
underwent a final helium flash in late 1994, has been carried out since
1996 February. The light curves show that Sakurai's Object is
continuously cooling while it slowly expands and slightly increases its
luminosity. The distance is estimated to be 8 kpc, the interstellar
extinction EB-V=0.53, and the luminosity in early 1997 is 10
000Lsun. The high luminosity indicates that the white dwarf
is quite massive. With the assumption of a slightly accelerated
photospheric expansion a realistic description of the outburst light
curve is achieved. Superimposed on the gradual brightness changes are
variations with amplitudes of up to 0.1 mag and cycle lengths of 63, 23,
14, and 8 days. In spite of the fact that no persistent periodicities
could be detected, pulsational studies show that such cyclic changes can
be used to constrain stellar parameters such as mass, luminosity, and
The Astronomical Journal 09/1997; 114:1657. · 4.97 Impact Factor