Detection and evolution of the CO (Δv= 2) emission in Nova V2615 Ophiuchi (2007)

We present near-infrared (1–2.5 μm) spectroscopic and photometric results of Nova V2615 Ophiuchi which was discovered in outburst in 2007 March. Our observations span a period of ∼80 d starting from 2007 March 28 when the nova was at its maximum light. The evolution of the spectra is shown from the initial P Cygni phase to an emission-line phase and finally to a dust formation stage. The characteristics of the JHK spectra are very similar to those observed in a nova outburst occurring on a carbon–oxygen white dwarf. We analyse an observed line at 2.088 μm and suggest that it could be due to Fe  ii excited by Lyman α fluorescence. The highlight of the observations is the detection of the first overtone bands of carbon monoxide (CO) in the 2.29–2.40 μm region. The CO bands are modelled to estimate the temperature and mass of the emitting CO gas and also to place limits on the ¹²C/¹³C ratio. The CO bands are recorded over several epochs, thereby allowing a rare opportunity to study the evolution from a phase of constant strength through a stage when the CO is destroyed fairly rapidly. We compare the observed time-scales involved in the evolution of the CO emission and find a good agreement with model predictions that investigate the chemistry in a nova outflow during the early stages.     

A new look at the position of the 1604 Supernova (V843 Ophiuchi)

The position of the supernova of 1604 (V843 Oph) is re‐assessed, with relevant discussion pertaining to the present‐day remnant, 3C 358. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nature of the soft x-ray excess in the spectrum of RX J1037.5-5647

The source responsible for the soft x-ray excess in the emission spectrum of the pulsar RX J1037.5-5647 is associated with a hot spot on the surface of the neutron star near the base of an accretion column. The intensity of the emission from this source, however, only undergoes small (on the order of 15%) variations, while the intensity of the hard component varies substantially with the rotation period of the neutron star. We show that this situation can occur if the angle between the axis of rotation and the magnetic axis of the neutron star is no more than 8°. The variation in the intensity of the hard component of the radiation in this case is interpreted in terms of an anisotropy in the directional diagram. In this scenario, the angle of inclination of the orbit of the binary system is close to 10°.     

Spectral evolution of Nova V400 Per (1974) and Nova V373 Sct (1975)

Photographic and spectroscopic observations of the two galactic novae, V400 Per and V373 Sct, which appeared in 1974 and 1975, have been carried out at Asiago. The light curves of the two novae were characterized by the presence of brightness oscillations during the early decline. The spectral evolution was quite normal: the spectra showed at first, over a relatively strong continuum, wide emission bands of moderate excitation, accompanied by blueshifted absorptions, with radial velocities of –1760 km s^–1 (Nova Per) and –1260 km s^–1 (Nova Sct). Later, after the novae entered the nebular stage, the continuum weakened, the absorption disappeared and the novae displayed the usual emission spectrum, with permitted and forbidden lines of high excitation ([Oiii], Niii, Hei, Heii). Forbidden lines of Fevi and Fevii-and in Nova Sct, also Fex and Ax-were present for a time, but they soon disappeared, so that at the end the spectrum was dominated by the [Oiii] nebular lines, even stronger than H.     

爆后新星武仙V 533的光度研究

老新星武仙V533(V533Her=武仙1963年新星)是一颗光度变化极其复杂的天体。本文给出了我们用双筒天体照相仪于1980年6月至1982年11月间对其所做的照相观测结果。从所得结果可以看到:(1)该星亮度在此期间已基本恢复到其爆前的宁静期亮度;(2)高时频观测指出V533 Her具有时标为小时级,变幅Δm～0.2~m的小幅度光变;(3)在此期间其亮度有上升趋势,上升幅度～1.5等。本文还讨论了V533 Her在爆发前后的光度变化情况,通过分析指出新星在爆发前可能有可觉察的光度变化。     

Spectrographic study of Nova Vulpeculae 1976 (NQ VUL)

Nova Vulpeculae was observed from November 11 to December 16, 1976, at the Beijing Observatory with the grating spectrograph attached to the Cassegrain focus of the 60/90 Schmidt telescope.This paper gives the idectification of the spectral features, the expansion velocities, the photoionization temperatures, the colour temperatures and the Balmer decrement. In wavelength range λλ 3400 – 6700 the principal lines are of HI, FeII, NaI, NII, CaII, TiII, [OI], [NII] atoms or ions. The majority of lines are of P Cyg type. The expansion velocities as derived from measurements of the absorption spectra amount to about 500 – 2200 km/s. Photoionisation temperatures are higher than the corresponding colour temperatures. They increased as the nova became fainter.     

V723 Cas (Nova Cassiopeiae 1995): MERLIN observations from 1996 to 2001

MERLIN observations of the unusually slow nova V723 Cas are presented. Nine epochs of 6-cm data between 1996 and 2001 are mapped, showing the initial expansion and brightening of the radio remnant, the development of structure and the final decline. A radio light curve is presented and fitted by the standard Hubble flow model for radio emission from novae in order to determine the values of various physical parameters for the shell. The model is consistent with the overall development of the radio emission. Assuming a distance of 2.39 (±0.38) kpc and a shell temperature of 17 000 K, the model yields values for expansion velocity of  414 ± 0.1 km s^-1  and shell mass of  1.13 ± 0.04 × 10⁻⁴ M_⊙  . These values are consistent with those derived from other observations although the ejected masses are rather higher than theoretical predictions. The structure of the shell is resolved by MERLIN and shows that the assumption of spherical symmetry in the standard model is unlikely to be correct.     

The remnant of Nova Cassiopeiae 1993 (V705 Cassiopeiae)

We have detected radio emission from the remnant of V705 Cas, beginning 221 d after visual maximum. We follow the remnant from first detection while still optically thick through the turn-over to optically thin emission, and finally confirming the absence of emission due to expansion and fading by the end of 1998. While the emission is consistent with thermal bremsstrahlung, as seen in most previous novae, the small-scale structure shows two ridge-like features, which develop significantly from day 585 until our last detection on day 1544. While the development is fairly rapid, it is also much smoother than that seen in V1974 Cyg, in that we can follow individual features as they change over almost 1000 d. Our optical spectra unequivocally indicate some form of axial symmetry, as derived from the velocity structure. This is difficult to reconcile with the observed development in the radio images. We suggest a number of possible explanations.     

Spectrographic study of Nova Cygni 1978 (V1668 CYG)

Nova Cygni 1978 was observed from October 11 to December 23, 1978 at the Beijing Observatory with the grating spectrograph attached to the Naismith focus of the Schmidt telescope. This paper gives postmaximum photographic magnitudes, identification of the spectral features, emission line structures, intensity ratios of some emission lines and the temperature of the underlying star.The main spectral lines in wavelength range from October 11 to 30 are those of the following atoms or ions: H, FeII, NII, TiII, [0I], NIII. From November 10, lines of [0III], HeI and Hell become visible one after the other. The emission line H_α shows three components of which the most redshifted is the strongest. In turn, each component is split into a number of secondary peaks. Temperature of the underlying star increases with decline of the nova brightness. The upper limit of temperature may be 120000 K.     

The early spectroscopy of V2670 Oph (Nova Oph 2008)

We report the spectroscopic observations of nova V2670 Oph secured at the Loiano Observatory, Italy, 39 days after the outburst. The spectra of V2670 Oph showed auroral lines, suggesting that ionization was increasing. V2670 Oph is a fast nova, with a decline rate by three magnitudes of 42 days. We have estimated the absolute magnitude at maximum and the distance of V2670 Oph. The nova achieved an absolute magnitude at maximum in the interval −7.9,…,−7.4. The distance of V2670 Oph is in the range 4.7–5.8 kpc.     

Chaplygin gas of Tachyon Nature Imposed by Noether Symmetry and constrained via H(z) data

An action of general form is proposed for a Universe containing matter, radiation and dark energy. The latter is interpreted as a tachyon field non-minimally coupled to the scalar curvature. The Palatini approach is used when varying the action so the connection is given by a more generic form. Both the self-interaction potential and the non-minimally coupling function are obtained by constraining the system to present invariability under global point transformation of the fields(Noether Symmetry). The only possible solution is shown to be that of minimal coupling and constant potential(Chaplygin gas). The behavior of the dynamical properties of the system is compared to recent observational data, which infers that the tachyon field must indeed be dynamical.     

Nature of the background ultraviolet radiation field at high redshifts

We have tried to determine the flux of the ultraviolet background radiation field from the column density ratios of various ions in several absorption systems observed in the spectra of QSOs. We find that in most cases the flux is considerably higher than what has been estimated to be contributed by the AGNs. The excess flux could originate locally in hot stars. In a few cases we have been able to show that such galactic flux can only contribute a part of the total required flux. The results suggest that the background gets a significant contribution from an unseen QSO population.     

Infrared radiation from dust in the H II region-molecular cloud complex S 252

A detailed study is made on the variation of the 12 μm emission of the H-II region-molecular cloud complex S 252 with the radiation field, using the IRAS data. The results show that, in order to explain the excess short wave emission, we must consider non-equilibrium emission by very small dust particles (PAHs and other small particles). These small grains emit 36% of the total infrared luminosity, mostly in the range shorter than 25 μm. The PAHs are severely depleted by the radiation field in the H-II region; in the dense cloud, they are less so because of the shielding by the cloud. A model incorporating a radial distribution of PAHs in the H-II region can satisfactorily explain the observed spatial variation of the 12 μm emission.     

Near-infrared and optical studies of the fast nova V4643 Sgr (Nova Sagittarii 2001)

It is generally accepted that the presence of a hot magnetic corona provides the source of X-ray emission in cool stars. With this connection one could expect to see the variation of magnetic flux in the activity cycle of a star mirrored by a similar variation in the stars X-ray emission. Using magnetic maps produced from flux emergence and transport simulations and assuming a potential field for the corona, we can extrapolate the coronal magnetic field and hence calculate the variation of the X-ray emission. We consider three types of activity cycle that successfully reproduce the pattern of intermingled magnetic flux at high latitudes, a feature observed with Zeeman–Doppler imaging. The three different cycles take the form of (1) an enhanced butterfly pattern where flux emergence is extended to a latitude of 70°, (2) an extended emergence profile as before but with an overlap of 4 yr in the butterfly diagram and (3) where no butterfly diagram is used. The cyclic variation in the X-ray emission is around two orders of magnitude for cases (1) and (3), but less than one order of magnitude for case (2). For all three cases, the rotational modulation of the X-ray emission is greatest at cycle minimum, but the emission measure weighted density varies little over the cycle. For cases (1) and (2) the fraction of the total flux that is open (along which a wind can escape) varies little over the cycle, but for case (3) this is three times larger at cycle minimum than at maximum. Our results clearly show that although magnetic cycles may exist for stars they are not necessarily observable in the X-ray emission.     

Deductions from the Indication of Eclipses of Nova V1493 Aql

Our mainly R band photometry of V1493 Aql (1999) during its outburst, indicates periodic variations with a period of 0.156 days, seen only 5 days after the maximum in V. This period can be orbital. The light curve indicates in addition, the presence of a faint eclipse like feature. We try to explain its extremely low amlitude, as being due to the eclipse of an expanded white dwarf component of the binary below an optically thick wind. We discuss what conditions would be required for such an interpretation to work.     

The spectroscopic evolution of V459 Vul (Nova Vul 2007 #2)

We report the spectroscopic follow-up of the nova V459 Vul carried out at the Loiano Observatory, Italy, at three epochs after the outburst. The spectroscopy showed high ionization lines of iron. The photometry has been used to estimate the absolute magnitude at maximum and the distance of the nova. V459 Vul is a fast nova, with decline times by two and three magnitudes of 18 and 30 days respectively. The nova achieved an absolute magnitude at maximum of ?8.7…?7.7. The distance of V459 Vul is in the range 2.3–5.0 kpc.     

The early spectroscopic evolution of nova V458 Vul (Nova Vulpeculae 2007)

The early spectral evolution of the nova V458 Vul has been monitored at the Loiano Observatory, Italy. The nova exhibited a couple of oscillations during the decline from initial maximum. We have performed spectroscopic observations to study the physical properties of the ejected material. The photometric light curve has been used to derive the nova distance and its absolute magnitude at maximum. V458 Vul is a fast nova, with decline rates by two or three magnitudes of 7 and 15 days respectively. The magnitude at maximum is M _V =?8.8. The nova distance is in the range 6.7–10.3 kpc. The spectra secured a few days after initial maximum showed emission lines of H I and Fe II, making V458 Vul a Fe II nova at this stage. After the oscillations V458 Vul came back to a standard decline curve, but evolved towards the He/N class. Thus V458 Vul is a hybrid nova.     

Some features of the pulsed radiation from the pulsar 1919+21 at 16.7, 20 and 25 MHz

An intense interpulse radio frequency radiation of PSR 1919+21 has been detected in the range of 16.7, 20 and 25 MHz. An integrated waveform of this radiation was investigated with time resolutions ofT/16 andT/64, and several characteristic regions of the intensity maxima and minima have been revealed. As has been shown, the maximum number of the best pronounced interpulses is about four, their location being symmetrical relative to the centre of the main pulse. The fine frequency structure of the integrated radiation was also investigated. It has been found that the shape of the signal can differ considerably with a frequency diversity of 10 to 100 kHz and only slightly with a separation of 5 to 10 MHz, the difference diminishing with an increase of the observation bandwidth and of the averaging time. Pulse broadening was studied at 16.7 and 25 MHz and has been found to agree with the interstellar scattering mechanism. The mean intensity of the main pulse and the interpulses has been evaluated and an essential difference of their spectral indices established.