arXiv subjects

M. F. Bode

Publications and source records attributed to M. F. Bode.

At least 55 records · Page 3Linked to original sources

arXiv2014

A remarkable recurrent nova in M31 - The X-ray observations

Another outburst of the recurrent M31 nova M31N 2008-12a was announced in late November 2013. Optical data suggest an unprecedentedly short recurrence time of approximately one year. In this Letter we address the X-ray properties of M31N 2008-12a. We requested Swift monitoring observations shortly after the optical discovery. We estimated source count rates and extracted X-ray spectra from the resulting data. The corresponding ultraviolet (UV) data was also analysed. M31N 2008-12a was clearly detected as a bright supersoft X-ray source (SSS) only six days after the well-constrained optical discovery. It displayed a short SSS phase of two weeks duration and an exceptionally hot X-ray spectrum with an effective blackbody temperature of ~97 eV. During the SSS phase the X-ray light curve displayed significant variability that might have been accompanied by spectral variations. The very early X-ray variability was found to be anti-correlated with simultaneous variations in the UV flux. The X-ray properties of M31N 2008-12a coherently point towards a high-mass white dwarf in the nova system. This object might be a promising Type Ia supernova progenitor. We re-discovered additional X-ray detections of M31N 2008-12a that are consistent with our data and increase the number of known nova outbursts to seven. This nova is an exceptional object that merits further attention in the future.

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arXiv2014

A remarkable recurrent nova in M31 - The optical observations

Context: In late November 2013 a fifth eruption in five years of the M31 recurrent nova M31N 2008-12a was announced. Aims: In this Letter we address the optical lightcurve and progenitor system of M31N 2008-12a. Methods: Optical imaging data of the 2013 eruption from the Liverpool Telescope, La Palma, and Danish 1.54m Telescope, La Silla, and archival Hubble Space Telescope near-IR, optical and near-UV data are astrometrically and photometrically analysed. Results: Photometry of the 2013 eruption, combined with three previous eruptions, enabled construction of a template light curve of a very fast nova, t2(V)~4 days. The archival data allowed recovery of the progenitor system in optical and near-UV data, indicating a red-giant secondary with bright accretion disk, or alternatively a system with a sub-giant secondary but dominated by a disk. Conclusions: The eruptions of M31N 2008-12a, and a number of historic X-ray detections, indicate a unique system with a recurrence timescale of ~1 year. This implies the presence of a very high mass white dwarf and a high accretion rate. The recovered progenitor system is consistent with such an elevated rate of accretion.We encourage additional observations, especially towards the end of 2014.

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arXiv2014

The Detailed Photometric and Spectroscopic Study of the 2011 Outburst of the Recurrent Nova T Pyxidis from 0.8 to 250 Days after Discovery

We investigated the optical lightcurve of T Pyx during its 2011 outburst by compiling a database of SMEI and AAVSO observations. The SMEI lightcurve, providing unprecedented detail covering 1.5-49d post-discovery, was divided into four phases based on the idealised CN optical lightcurve; the initial rise (1.5-3.3d), the pre-maximum halt (3.3-13.3d), the final rise (14.7-27.9d), and the early decline (27.9d-). The SMEI lightcurve contains a strongly detected period of 1.44+/-0.05d during the pre-maximum phase. These oscillations resemble those found in TNR models arising from instabilities in the expanding envelope. No spectral variation mirroring the lightcurve periodicity was found. A marked dip at 22-24d just before maximum light (27.9d) may represent the same phenomenon seen in novae observed by SMEI. Spectra from the Liverpool Telescope and SMARTS 1.5m were obtained from 0.8-80.7 and 155.1-249.9d, covering the major phases of development. A distinct high velocity ejection phase was evident during the early rise (V~4000 km/s). A marked drop at 5.7d, and then a gradual increase occurred in the ejection velocity which stabilised at ~1500 km/s at the pre-maximum halt. Here we propose two stages of mass loss, a short-lived phase occurring immediately after outburst, lasting ~6d, followed by a steadily evolving and higher mass loss phase. The overall spectral development follows that typical of a CN and comparison with the photometric behaviour reveals consistencies with the evolving pseudo-photosphere model of a CN outburst. Comparing optical spectra to X-ray and radio lightcurves, weak [Fe X] 6375 Angstrom emission was marginally detected before the X-ray rise and was clearly present during the brightest phase of X-ray emission. If the onset of the X-ray phase and the start of the optical final decline are related to the cessation of significant mass loss, then this occurred at 90-110d.

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arXiv2013

Obscuration effects in Super-Soft-Source X-ray spectra

Super-Soft-Source (SSS) X-ray spectra are blackbody-like spectra with effective temperatures ~3-7x10^5 K and luminosities of 10^{35-38} erg/s. SSS grating spectra display atmospheric absorption lines. Radiation transport atmosphere models can be used to derive physical parameters, but more sophisticated models are required. We bypass the complications of spectral models and concentrate on the data in a comparative, qualitative study. We inspect all available X-ray grating SSS spectra to determine systematic, model-independent trends. We use comparative plots of spectra of different systems to find common and different features. The results are interpreted in the context of system parameters obtained from the literature. We find two distinct types of SSS spectra which we name SSa and SSe. Their main observational characteristics are either clearly visible absorption lines or emission lines, respectively, while both types contain atmospheric continuum emission. SSe may be obscured SSa systems, which is supported by similarities between SSe and SSa with obscured and unobscured AGN, respectively. Further, we find all known or suspected high-inclination systems to emit permanently in an SSe state. Some sources are found to transition between SSa and SSe states, becoming SSe when fainter. SSS spectra are subject to various occultation processes. In Cal 87, the accretion disc blocks the central hot source when viewed edge on. In novae, the accretion disc may have been destroyed during the initial explosion but could have reformed by the time of the SSS phase. In addition, clumpy ejecta may lead to temporary obscuration events. The emission lines originate from reprocessed emission in the accretion disc, its wind or further out in clumpy ejecta while Thomson scattering allows continuum emission to be visible also during total obscuration of the central hot source.

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arXiv2013

Rapid Dust Formation in Novae: The Speed Class - Formation Timescale Correlation Explained

Observations show that the time of onset of dust formation in classical novae depends strongly on their speed class, with dust typically taking longer to form in slower novae. Using empirical relationships between speed class, luminosity and ejection velocity, it can be shown that dust formation timescale is expected to be essentially independent of speed class. However, following a nova outburst the spectrum of the central hot source evolves, with an increasing proportion of the radiation being emitted short-ward of the Lyman limit. The rate at which the spectrum evolves also depends on the speed class. We have therefore refined the simple model by assuming photons at energies higher than the Lyman limit are absorbed by neutral hydrogen gas internal to the dust formation sites, therefore preventing these photons reaching the nucleation sites. With this refinement the dust formation timescale is theoretically dependent on speed class and the results of our theoretical modification agree well with the observational data. We consider two types of carbon-based dust, graphite and amorphous carbon, with both types producing similar relationships. Our results can be used to predict when dust will form in a nova of a given speed class and hence when observations should optimally be taken to detect the onset of dust formation.

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arXiv2013

Extragalactic Nova Populations

Nova rates have now been measured for more than a dozen galaxies spanning a wide range of Hubble types. When normalized to the infrared K-band luminosity of the galaxy, the luminosity-specific nova rates typically fall in the range of 1-3 novae per year per 10^10 solar luminosities in K, and do not vary significantly across the Hubble sequence. Preliminary nova rates are presented for three Virgo ellipticals (M49, M84, and M87) with differing globular cluster specific frequencies. No dependence of the luminosity-specific nova rate on globular cluster specific frequency was found. Photometric and spectroscopic observations of novae in the Local Group suggest that galaxies dominated by a younger stellar population (M33 and the LMC) are characterized by novae with a generally faster photometric evolution, and by a higher fraction of He/N novae compared with novae in M31. The recurrent nova population in the LMC appears to be higher than that seen in M31 and the Galaxy.

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arXiv2013

Morpho-Kinematical Modelling of Nova Eridani 2009 (KT Eri)

Modelling the morphology of a nova outburst provides valuable information on the shaping mechanism in operation at early stages following the outburst. We performed morpho-kinematical studies, using {\sc shape}, of the evolution of the Hα line profile following the outburst of the nova KT Eridani. We applied a series of geometries in order to determine the morphology of the system. The best fit morphology was that of a dumbbell structure with a ratio between the major to minor axis of 4:1, with an inclination angle of 58$^{+6}_{-7}$ degrees and a maximum expansion velocity of 2800$\pm$200 km/s. Although, we found that it is possible to define the overall structure of the system, the radial density profile of the ejecta is much more difficult to disentangle. Furthermore, morphology implied here may also be consistent with the presence of an evolved secondary as suggested by various authors.

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arXiv2013

Spectroscopic and Photometric Development of T Pyxidis (2011) from 0.8 to 250 Days After Discovery

We investigated the optical light curve of T Pyx during its 2011 outburst through compiling a database of SMEI and AAVSO observations. The SMEI light curve, providing unprecedented detail with high cadence data during t=1.5-49 days post-discovery, was divided into four phases based on the idealised nova optical light curve; the initial rise, the pre-maximum halt (or the 'plateau'), the final rise, and the early decline. Variation in the SMEI light curve reveals a strongly detected period of 1.44\pm0.04 days before the visual maximum. The spectra from the LT and SMARTS telescopes were investigated during t=0.8-80.7 and 155.1-249.9 days. The nova was observed very early in its rise and a distinct high velocity ejection phase was evident. A marked drop and then gradual increase in derived ejection velocities were present. Here we propose two different stages of mass loss, a short-lived phase occurring immediately after outburst followed by a more steadily evolving and higher mass loss phase. The overall spectral development follows that typical of a Classical Nova and comparison to the photometric behaviour reveals consistencies with the simple evolving pseudo-photosphere model of the nova outburst. The optical spectra are also compared to X-ray and radio light curves. Weak [Fe X] 6375A emission was marginally detected before the rise in X-ray emission. The middle of the plateau in the X-ray light curve is coincident with the appearance of high ionization species detected in optical spectra and the peak of the high frequency radio flux.

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arXiv2013

On the Galactic Nova Progenitor Population

Of the 350 or more known Galactic classical novae, only a handful of them, the recurrent novae, have been observed in outburst more than once. At least eight of these recurrents are known to harbour evolved secondary stars, rather than the main sequence secondaries typical in classical novae. Here we present a selection of the work and rationale that led to the proposal of a new nova classification scheme based not on the outburst properties but on the nature of the quiescent system. Also outlined are the results of a photometric survey of a sample of quiescent Galactic novae, showing that the evolutionary state of the secondary can be easily determined and leading to a number of predictions. We discuss the implications of these results, including their relevance to extragalactic work and the proposed link to type Ia supernovae. We also present a summary of the work using the SMEI instrument to produce exquisite nova light-curves and confirmation of the pre-maximum halt.

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arXiv2013

On the M31 Nova Progenitor Population

We present a survey of M31 novae in quiescence. This is the first catalogue of extragalactic systems in quiescence and contains 37 spectroscopically confirmed novae from 2006 to 2013. We used Liverpool Telescope and Faulkes Telescope North images taken during outburst to identify accurate positions for each system. These positions were then transformed to archival Hubble Space Telescope (HST) images and we performed photometry on any resolvable source that was consistent with the transformed positions. As red giants in M31 will be resolvable in the HST images, we can detect systems with red giant secondaries. There are only a few confirmed examples of such systems in our Galaxy (e.g. RS Oph and T CrB). However, we find a much higher portion of the nova population in M31 may contain red giant secondaries. For some novae, coincident HST images had been taken when the nova was still fading, allowing us to produce light curves that go fainter than is possible to achieve for most extragalactic systems. Finally, we compare the M31 and Galactic quiescent nova populations.

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arXiv2012

An HI shell-like structure associated with nova V458 Vulpeculae?

We report the radio detection of a shell-like HI structure in proximity to, and probably associated with, the nova V458 Vul. High spectral resolution observation with the Giant Metrewave Radio Telescope has made it possible to study the detailed kinematics of this broken and expanding shell. Unlike the diffuse Galactic HI emission, this is a single velocity component emission with significant clumping at ~ 0.5' scales. The observed narrow line width of ~ 5 km/s suggests that the shell consists of mostly cold gas. Assuming a distance of 13 kpc to the system, as quoted in the literature, the estimated HI mass of the nebula is about 25 M_sun. However, there are some indications that the system is closer than 13 kpc. If there is a physical association of the HI structure and the nova system, the asymmetric morphology and the off-centred stellar system indicates past strong interaction of the mass loss in the asymptotic giant branch phase with the surrounding interstellar medium. So far, this is the second example, after GK Per, of a large HI structure associated with a classical nova.

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arXiv2012

The expanding dusty bipolar nebula around the nova V1280 Sco

V1280 Sco is one of the slowest dust-forming nova ever historically observed. We performed multi-epoch high-spatial resolution observations of the circumstellar dusty environment of V1280 Sco to investigate the level of asymmetry of the ejecta We observed V1280 Sco in 2009, 2010 and 2011 using unprecedented high angular resolution techniques. We used the NACO/VLT adaptive optics system in the J, H and K bands, together with contemporaneous VISIR/VLT mid-IR imaging that resolved the dust envelope of V1280 Sco, and SINFONI/VLT observations secured in 2011. We report the discovery of a dusty hourglass-shaped bipolar nebula. The apparent size of the nebula increased from 0.30" x 0.17" in July 2009 to 0.64" x 0.42" in July 2011. The aspect ratio suggests that the source is seen at high inclination. The central source shines efficiently in the K band and represents more than 56+/-5% of the total flux in 2009, and 87+/-6% in 2011. A mean expansion rate of 0.39+/-0.03 mas per day is inferred from the VISIR observations in the direction of the major axis, which represents a projected upper limit. Assuming that the dust shell expands in that direction as fast as the low-excitation slow ejecta detected in spectroscopy, this yields a lower limit distance to V1280 Sco of 1kpc; however, the systematic errors remain large due to the complex shape and velocity field of the dusty ejecta. The dust seems to reside essentially in the polar caps and no infrared flux is detected in the equatorial regions in the latest dataset. This may imply that the mass-loss was dominantly polar.

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arXiv2012

Infrared observations of the recurrent nova T Pyxidis: ancient dust basks in the warm glow of the 2011 outburst

We present Spitzer Space Telescope and Herschel Space Observatory infrared observations of the recurrent nova T Pyx during its 2011 eruption, complemented by ground-base optical-infrared photometry. We find that the eruption has heated dust in the pre-existing nebulosity associated with T Pyx. This is most likely interstellar dust swept up by T Pyx - either during previous eruptions or by a wind - rather than the accumulation of dust produced during eruptions.

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arXiv2012

On the Spectroscopic Classes of Novae in M33

We report the initial results from an ongoing multi-year spectroscopic survey of novae in M33. The survey resulted in the spectroscopic classification of six novae (M33N 2006-09a, 2007-09a, 2009-01a, 2010-10a, 2010-11a, and 2011-12a) and a determination of rates of decline (t_2 times) for four of them (2006-09a, 2007-09a, 2009-01a, and 2010-10a). When these data are combined with existing spectroscopic data for two additional M33 novae (2003-09a and 2008-02a) we find that 5 of the 8 novae with available spectroscopic class appear to be members of either the He/N or Fe IIb (hybrid) classes, with only two clear members of the Fe II spectroscopic class. This initial finding is very different from what would be expected based on the results for M31 and the Galaxy where Fe II novae dominate, and the He/N and Fe IIb classes together make up only ~20% of the total. It is plausible that the increased fraction of He/N and Fe IIb novae observed in M33 thus far may be the result of the younger stellar population that dominates this galaxy, which is expected to produce novae that harbor generally more massive white dwarfs than those typically associated with novae in M31 or the Milky Way.

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arXiv2011

On the Progenitors of Galactic Novae

Of the approximately 400 known Galactic classical novae, only ten of them, the recurrent novae, have been seen to erupt more than once. At least eight of these recurrents are known to harbor evolved secondary stars, rather than the main sequence secondaries typical in classical novae. In this paper, we propose a new nova classification system, based solely on the evolutionary state of the secondary, and not (like the current schemes) based on the properties of the outbursts. Using archival optical and near-infrared photometric observations of a sample of thirty eight quiescent Galactic novae we show that the evolutionary state of the secondary star in a quiescent system can predicted and several objects are identified for follow-up observations; CI Aql, V2487 Oph, DI Lac and EU Sct.

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arXiv2011

The Outbursts of Classical and Recurrent Novae

In this review, I present our current state of knowledge regarding both Classical Nova and Recurrent Nova systems. Two particular objects (V1974 Cyg and RS Oph) are chosen to illustrate the range of phenomena that may be associated with their outbursts. The wider importance of nova research is emphasised and some of the most pressing unsolved problems are summarised.

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arXiv2011

Classical and Recurrent Nova Outbursts

Over the last 40 years, multi-frequency observations, coupled with advances in theoretical modelling, have led to a much fuller understanding of the nova phenomenon. Here I give a brief review of the current state of knowledge of Classical and Recurrent Novae including their central systems; the causes and consequences of their outbursts; sub-types, and possible relationships to Type Ia Supernovae. Particular attention is paid to the Recurrent Nova RS Ophiuchi as it shows a wealth of phenomena associated with its 2006 outburst. Finally, some open questions and avenues for future work are summarised.

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arXiv2011

Historical light curve and search for previous outbursts of Nova KT Eridani (2009)

Context. Nova Eridani (2009) caught the eye of the nova community due to its fast decline from maximum, which was initially missed, and its subsequent development in the radio and X-ray wavelengths. This system also exhibits properties similar to those of the much smaller class of recurrent novae; themselves potential progenitors of Type Ia Supernovae. Aims. We aim to determine the nature and physical parameters of the KT Eri progenitor system. Methods. We searched the Harvard College Observatory archive plates for the progenitor of KT Eri to determine the nature of the system, particularly the evolutionary stage of the secondary.We used the data obtained to search for any periodic signal and the derived luminosity to estimate a recurrence timescale. Furthermore, by comparing the colours of the quiescent system on a colour-magnitude diagram we may infer the nature of the secondary star. Results. We identified the progenitor system of KT Eri and measured a quiescent magnitude of < B >= 14.7 \pm 0.4. No previous outburst was found. However, we suggest that if the nova is recurrent it should be on a timescale of centuries. We find a periodicity at quiescence of 737 days which may arise from reflection effects and/or eclipses in the central binary. The periodicity and the quiescence magnitude of the system suggest that the secondary star is evolved and likely in, or ascending, the Red Giant Branch. A second period is evident at 376 days which has a sinusoidal like light curve. Furthermore, the outburst amplitude of ~ 9 magnitudes is inconsistent with those expected for fast classical novae (~ 17 magnitudes) which may lend further support for an evolved secondary. (Abridged)

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