T. Liimets

The peculiar optical spectrum of 4C+22.25: Imprint of a massive black hole binary?

We report the discovery of peculiar features in the optical spectrum of 4C+22.25, a flat spectrum radio quasar at z = 0.4183 observed in the Sloan Digital Sky Survey and in a dedicated spectroscopic follow-up from the Nordic Optical Telescope. The Hβ and Hα lines show broad profiles (FWHM ~ 12,000 km s–1), faint fluxes, and extreme offsets (Δv = 8700 ± 1300 km s–1) with respect to the narrow emission lines. These features show no significant variation in a time lag of ~3.1 yr (rest frame). We rule out possible interpretations based on the superposition of two sources or on recoiling black holes, and discuss the virtues and limitations of a massive black hole binary scenario.

WATER-ICE-DRIVEN ACTIVITY ON MAIN-BELT COMET P/2010 A2 (LINEAR)?

The dust ejecta of Main-Belt Comet P/2010 A2 (LINEAR) have been observed with several telescopes at the Observatorio del Roque de los Muchachos on La Palma, Spain. Application of an inverse dust tail Monte Carlo method to the images of the dust ejecta from the object indicates that a sustained, likely water-ice-driven, activity over some eight months is the mechanism responsible for the formation of the observed tail. The total amount of the dust released is estimated to be 5 × 107 kg, which represents about 0.3% of the nucleus mass. While the event could have been triggered by a collision, this cannot be determined from the currently available data.

Eclipse of the B3V companion and flaring of emission lines in V838 Monocerotis

After four years during which only the spectacular light echo was showing continuous and rapid evolution while the central star was nearly constant, in autumn 2006 V838 Mon began a sequence of events which profoundly altered its spectroscopic and photometric behavior: (a) an eclipse of the B3V companion, characterized by the disappearance and reappearance of the B3V companion from optical spectra, and an eclipse-like lightcurve of ∼70 day duration and ∆B ∼ 1.15 mag, ∆V ∼ 0.55 mag, ∆RC ∼ 0.10 mag maximum depth; (b) a large increase in intensity of the [FeII] and FeII emission lines, and the appearance in emission for the first time since the 2002 outburst of Hα and higher Balmer series lines. While the [FeII] and FeII lines maintained a very sharp and unresolved profile, the Hα developed into a wide and structured profile, characterized by a sharp central reversal at the same velocity as one of the CO radio emission components. The disappearance of the B3V companion is equally well explained by a grazing eclipse from the outbursting L-type supergiant or by an eclipse from a dust cloud characterized by EB−V = 0.55 and RV = 3.1. We believe the flaring of the emission lines occurred at a similar time as the B3V eclipse just by chance.

The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst - II. The circumstellar environment and the aftermath

Context. The nova outburst of V407 Cyg in 2010 Mar. 10 was the first observed for this star but its close resemblance to the well known symbiotic-like recurrent nova RS Oph suggests that it is also a member of this rare type of Galactic novae. The nova was the first detected at γ-ray energies and is the first known nova explosion for this system. The extensive multiwavelength coverage of this outburst makes it an ideal comparison with the few other outbursts known for similar systems. Aims. We extend our previous analysis of the Mira and the expanding shock from the explosion to detail the time development of the photoionized Mira wind, circumstellar medium, and shocked circumstellar environment to derive their physical parameters and how they relate to large scale structure of the environment, extending the previous coverage to more than 500 days after outburst. Methods. We use optical spectra obtained at high resolution with the Nordic Optical Telescope (NOT) (R ≈ 45 000 to 65 000) and medium resolution Ondy Observatory (R ≈ 12 000) data and compare the line variations with publicly available archival measurements at 30 GHz OVNR and at X-rays with Swift during the first four months of the outburst, through the end of the epoch of strong XR emission. We use nebular diagnostics and high resolution profile variations to derive the densities and locations of the extended emission. Results. We find that the higher the ionization and/or the higher the excitation energy, the more closely the profiles resemble the He II/Ca V-type high velocity shock profile discussed in Paper I. This also accounts for the comparative development of the [N II] and [O III] isoelectronic transitions: the [O III] 4363 A profile does not show the low velocity peaks while the excited [N II] 5754 A does. If nitrogen is mainly N +3 or higher in the shock, the upper state of the [N II] nebular lines will contribute but if the oxygen is O +2 then this line is formed by recombination, masking the nebular contributor, and the lower states are collisionally quenched but emit from the low density surroundings. Absorption lines of Fe-peak ions formed in the Mira wind were visible as P Cyg profiles at low velocity before Day 69, around the time of the X-ray peak and we identified many absorption transitions without accompanying emission for metal lines. The H Balmer lines showed strong P Cyg absorption troughs that weakened during the 2010 observing period, through Day 128. The Fe-peak line profiles and flux variations were different for permitted and forbidden transitions: the E1 transitions were not visible after Day 128 but had shown a narrow peak superimposed on an extended (200 km s −1 ) blue wing, while the M1 and E2 transitions persisted to Day 529, the last observation, and showed extended redshifted wings up of the same velocity. We distinguish the components from the shock, the photoionized environment, and the chromosphere and inner Mira wind using spectra taken more than one year after outburst. The multiple shells and radiative excitation phenomenology are similar to those recently cited for GRBs and SNIa.

A new planetary nebula in the outer reaches of the galaxy

Aims. A proper determination of the abundance gradient in the Milky Way requires the observation of objects at large galactiocentric distances. With this aim, we are exploring the planetary nebula population towards the Galactic anticentre. In this article, the discovery and physico-chemical study of a new planetary nebula towards the anticentre direction, IPHASX J052531.19+281945.1 (PNG 178.1-04.0), is presented. Methods. The planetary nebula was discovered from the IPHAS survey. Long-slit follow-up spectroscopy was carried out to confirm its planetary nebula nature and to calculate its physical and chemical characteristics. Results. The newly discovered planetary nebula turned out to be located at a very large galactocentric distance (DGC = 20.8±3.8 kpc), larger than any previously known planetary nebula with measured abundances. Its relatively high oxygen abundance (12+log(O/H) = 8.36 ± 0.03) supports a flattening of the Galactic abundance gradient at large galactocentric distances rather than a linearly decreasing gradient.

The ongoing outburst of the new symbiotic star IPHASJ190832.31+051226.6

Aims. Eleven new symbiotic stars have recently been discovered with IPHAS, the INT Hα survey of the Northern Galactic plane. The star IPHAS J190832.31+051226.6 was proposed as an additional candidate on the basis of the existing spectrum. Here, we investigate the nature of this source by means of additional observations. Methods. Photometric data, optical spectra obtained in 2006 and 2009, a higher resolution spectrum resolving the Hα profile, and near-IR spectra of IPHAS J190832.31+051226.6 are all presented. Results. The source brightened in the r band by 2.3 mag from 2004 to 2009. From 2006 to 2009, the spectrum has evolved from one with the obvious continuum of an M giant star plus HI and HeI lines in emission to a lower excitation nebular spectrum with HI, CaII, and FeII emission and a bluer continuum in which the absorption bands of the red giant are only visible at wavelengths longer than 7500 A. The Hα line is broad with a deep central absorption and extended wings. Conclusions. The averaged rate of the brightness increase, the rise of a blue continuum overwhelming the absorption bands of the M giant, and the corresponding decline of the ionization condition of the emission-line spectrum, are all consistent with the hypothesis that IPHAS J190832.31+051226.6 is a new symbiotic star picked up during the onset of a symbiotic nova outburst that is still in progress at the time of writing.

New insights into the outflows from R Aquarii

R Aquarii is a symbiotic binary surrounded by a large and complex nebula with a prominent curved jet. It is one of the closest known symbiotic systems, and therefore offers a unique opportunity to study the central regions of these systems and the formation and evolution of astrophysical jets. We studied the evolution of the central jet and outer nebula of R Aqr taking advantage of a long term monitoring campaign of optical imaging, as well as of high-resolution integral field spectroscopy. Narrow-band images acquired over a period of more than 21 years are compared in order to study the expansion and evolution of all components of the R Aqr nebula. The magnification method is used to derive the kinematic ages of the features that appear to expand radially. Integral field spectroscopy of the OIII 5007A emission is used to study the velocity structure of the central regions of the jet. New extended features, further out than the previously known hourglass nebula, are detected. The kinematic distance to R Aqr is calculated to be 178 pc using the expansion of the large hourglass nebula. This nebula of R Aqr is found to be roughly 650 years old, while the inner regions have ages ranging from 125 to 290 years. The outer nebula is found to be well described by a ballistic expansion, while for most components of the jet strong deviations from such behaviour are found. We find that the Northern jet is mostly red-shifted while its Southern part is blue-shifted, apparently at odds with findings from previous studies but almost certainly a consequence of the complex nature of the jet and variations in ionisation and illumination between observations.

The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst

Context. V407 Cyg was, before 2010 Mar., known only as a D-type symbiotic binary system in which the Mira variable has a pulsation period of approximately 750 days, one of the longest known. On 2010 Mar. 10, it was discovered in outburst, eventually reaching V < 8. This is the first recorded nova event for this system, but it closely resembles the spectroscopic development of RS Oph, the prototypical symbiotic-like recurrent nova. It was also detected by Fermi above 100 MeV and displayed strong, likely nonthermal centimeter wavelength radio emission. Aims. Unlike classical novae occurring in compact cataclysmic binary systems, for which the ejecta undergo free ballistic expansion, this explosion occurred within the dense, complex wind of a Mira variable companion. This paper concentrates on the development of the shock and its passage through the Mira wind. We also present some constraints on the binary system properties. Methods. Using medium and high resolution ground-based optical spectra, visual and Swift UV photometry, and Swift X-ray spectrophotometry, we describe the behavior of the high-velocity profile evolution for this nova during its first three months. Results. Using the diffuse interstellar bands visible in the high-resolution optical spectra, we obtain an extinction E(B - V) ≈ 0.45 ± 0.05. The spectral type of the red giant during this period, when the star was at R minimum, was no earlier than M7 III. The peak of the X-ray emission occurred at about day 40 with a broad maximum and decline after day 50. The main changes in the optical spectrum began at around that time. The He II 4686 A line first appeared between days 7 and 14 and initially displayed a broad, symmetric profile that is characteristic of all species before day 60. The profile development thereafter depended on ionization state. Low-excitation lines remained comparatively narrow, with v rad,max of order 200-400 km s -1 . They were systematically more symmetric than lines such as [Ca V], [Fe VII], [Fe X], and He II, all of which showed a sequence of profile changes going from symmetric to a blue wing similar to that of the low ionization species but with a red wing extended to as high as 600 km s -1 . The [O I] 6300, 6364 doublet showed a narrow wind-emission component near the rest velocity of the system and a broad component, 200-300 km s -1 , whose relative intensity increased in time. Forbidden lines of N II and O III had two separate contributors to the profiles, a broad line that increased in strength and velocity width, exceeding 200 km s -1 , and narrow components from a surrounding ionized region at higher velocity than the Mira wind. The Na I D doublet developed a broad component with similar velocity width to the other low-ionization species. The O VI Raman features observed in recent outbursts of RS Oph were not detected. We interpret these variations as aspherical expansion of the ejecta within the Mira wind. The blue side is from the shock penetrating into the wind while the red wing is from the low-density periphery. The maximum radial velocities obey power laws, v max ~ t -n with n ≈ 1/3 for red wing and ≈0.8 for the blue.

The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst: I. the shock and its evolution

Context. V407 Cyg was, before 2010 Mar., known only as a D-type symbiotic binary system in which the Mira variable has a pulsation period of approximately 750 days, one of the longest known. On 2010 Mar. 10, it was discovered in outburst, eventually reaching V < 8. This is the first recorded nova event for this system, but it closely resembles the spectroscopic development of RS Oph, the prototypical symbiotic-like recurrent nova. It was also detected by Fermi above 100 MeV and displayed strong, likely nonthermal centimeter wavelength radio emission. Aims. Unlike classical novae occurring in compact cataclysmic binary systems, for which the ejecta undergo free ballistic expansion, this explosion occurred within the dense, complex wind of a Mira variable companion. This paper concentrates on the development of the shock and its passage through the Mira wind. We also present some constraints on the binary system properties. Methods. Using medium and high resolution ground-based optical spectra, visual and Swift UV photometry, and Swift X-ray spectrophotometry, we describe the behavior of the high-velocity profile evolution for this nova during its first three months. Results. Using the diffuse interstellar bands visible in the high-resolution optical spectra, we obtain an extinction E(B - V) ≈ 0.45 ± 0.05. The spectral type of the red giant during this period, when the star was at R minimum, was no earlier than M7 III. The peak of the X-ray emission occurred at about day 40 with a broad maximum and decline after day 50. The main changes in the optical spectrum began at around that time. The He II 4686 A line first appeared between days 7 and 14 and initially displayed a broad, symmetric profile that is characteristic of all species before day 60. The profile development thereafter depended on ionization state. Low-excitation lines remained comparatively narrow, with v rad,max of order 200-400 km s -1 . They were systematically more symmetric than lines such as [Ca V], [Fe VII], [Fe X], and He II, all of which showed a sequence of profile changes going from symmetric to a blue wing similar to that of the low ionization species but with a red wing extended to as high as 600 km s -1 . The [O I] 6300, 6364 doublet showed a narrow wind-emission component near the rest velocity of the system and a broad component, 200-300 km s -1 , whose relative intensity increased in time. Forbidden lines of N II and O III had two separate contributors to the profiles, a broad line that increased in strength and velocity width, exceeding 200 km s -1 , and narrow components from a surrounding ionized region at higher velocity than the Mira wind. The Na I D doublet developed a broad component with similar velocity width to the other low-ionization species. The O VI Raman features observed in recent outbursts of RS Oph were not detected. We interpret these variations as aspherical expansion of the ejecta within the Mira wind. The blue side is from the shock penetrating into the wind while the red wing is from the low-density periphery. The maximum radial velocities obey power laws, v max ~ t -n with n ≈ 1/3 for red wing and ≈0.8 for the blue.

The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst I. The shock and its evolution

Context. V407 Cyg was, before 2010 Mar., known only as a D-type symbiotic binary system in which the Mira variable has a pulsation period of approximately 750 days, one of the longest known. On 2010 Mar. 10, it was discovered in outburst, eventually reaching V < 8. This is the first recorded nova event for this system, but it closely resembles the spectroscopic development of RS Oph, the prototypical symbiotic-like recurrent nova. It was also detected by Fermi above 100 MeV and displayed strong, likely nonthermal centimeter wavelength radio emission. Aims. Unlike classical novae occurring in compact cataclysmic binary systems, for which the ejecta undergo free ballistic expansion, this explosion occurred within the dense, complex wind of a Mira variable companion. This paper concentrates on the development of the shock and its passage through the Mira wind. We also present some constraints on the binary system properties. Methods. Using medium and high resolution ground-based optical spectra, visual and Swift UV photometry, and Swift X-ray spectrophotometry, we describe the behavior of the high-velocity profile evolution for this nova during its first three months. Results. Using the diffuse interstellar bands visible in the high-resolution optical spectra, we obtain an extinction E(B - V) ≈ 0.45 ± 0.05. The spectral type of the red giant during this period, when the star was at R minimum, was no earlier than M7 III. The peak of the X-ray emission occurred at about day 40 with a broad maximum and decline after day 50. The main changes in the optical spectrum began at around that time. The He II 4686 A line first appeared between days 7 and 14 and initially displayed a broad, symmetric profile that is characteristic of all species before day 60. The profile development thereafter depended on ionization state. Low-excitation lines remained comparatively narrow, with v rad,max of order 200-400 km s -1 . They were systematically more symmetric than lines such as [Ca V], [Fe VII], [Fe X], and He II, all of which showed a sequence of profile changes going from symmetric to a blue wing similar to that of the low ionization species but with a red wing extended to as high as 600 km s -1 . The [O I] 6300, 6364 doublet showed a narrow wind-emission component near the rest velocity of the system and a broad component, 200-300 km s -1 , whose relative intensity increased in time. Forbidden lines of N II and O III had two separate contributors to the profiles, a broad line that increased in strength and velocity width, exceeding 200 km s -1 , and narrow components from a surrounding ionized region at higher velocity than the Mira wind. The Na I D doublet developed a broad component with similar velocity width to the other low-ionization species. The O VI Raman features observed in recent outbursts of RS Oph were not detected. We interpret these variations as aspherical expansion of the ejecta within the Mira wind. The blue side is from the shock penetrating into the wind while the red wing is from the low-density periphery. The maximum radial velocities obey power laws, v max ~ t -n with n ≈ 1/3 for red wing and ≈0.8 for the blue.