A paper on the long cycle variability of the Algol OGLE-LMC-DPV-065 has been accepted in MNRAS

May 13th, 2019 / No Comments » / by Vitaly

The paper entitled “On the long cycle variability of the Algol OGLE-LMC-DPV-065 and its stellar, orbital and disk parameters” has been accepted for publication in MNRAS.
Preprint: ArXiv:1905.04231.

Mennickent R. E., …, Neustroev V. V., et al.
Abstract:
OGLE-LMC-DPV-065 is an interacting binary whose double-hump long photometric cycle remains hitherto unexplained. We analyze photometric time series available in archive datasets spanning 124 years and present the analysis of new high-resolution spectra. A refined orbital period is found of 10\fd0316267 ± 0\fd0000056 without any evidence of variability. In spite of this constancy, small but significant changes in timings of the secondary eclipse are detected. We show that the long period continuously decreases from 350 to 218 days during 13 years, then remains almost constant for about 10 years. Our study of radial velocities indicates a circular orbit for the binary and yields a mass ratio of 0.203 ± 0.001. From the analysis of the orbital light curve we find that the system contains 13.8 and 2.81 \msun\ stars of radii 8.8 and 12.6 \rsun\ and absolute bolometric magnitudes -6.4 and -3.0, respectively. The orbit semi-major axis is 49.9 \rsun\ and the stellar temperatures are 25460 K and 9825 K. We find evidence for an optically and geometrically thick disk around the hotter star. According to our model, the disk has a radius of 25 \rsun, central and outer vertical thickness of 1.6 \rsun\ and 3.5 \rsun, and temperature of 9380 K at its outer edge. Two shock regions located at roughly opposite parts of the outer disk rim can explain the light curves asymmetries. The system is a member of the double periodic variables and its relatively high-mass and long photometric cycle make it similar in some aspects to β Lyrae.

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A paper on a high-proper motion cataclysmic variable imbedded in a bow-shock nebula has been accepted in MNRAS

April 1st, 2019 / Comments Off on A paper on a high-proper motion cataclysmic variable imbedded in a bow-shock nebula has been accepted in MNRAS / by Vitaly

The paper entitled “From outburst to quiescence: spectroscopic evolution of V1838 Aql imbedded in a bow-shock nebula” has been accepted for publication in MNRAS.
Preprint: ArXiv:1811.02349.

Hernandez Santisteban J. V., Echevarria J., Zharikov S., Neustroev V. V., et al.
Abstract:
We analyse new optical spectroscopic, direct-image and X-ray observations of the recently discovered a high proper motion cataclysmic variable V1838 Aql. The data were obtained during its 2013 superoutburst and its subsequent quiescent state. An extended emission around the source was observed up to 30 days after the peak of the superoutburst, interpreted it as a bow–shock formed by a quasi-continuous outflow from the source in quiescence. The head of the bow–shock is coincident with the high-proper motion vector of the source (v⊥=123±5 km/s) at a distance of d=202±7 pc. The object was detected as a weak X-ray source (0.015±0.002 counts/s) in the plateau of the superoutburst, and its flux lowered by two times in quiescence (0.007±0.002 counts/s). Spectroscopic observations in quiescence we confirmed the orbital period value Porb=0.0545±0.0026 days, consistent with early-superhump estimates, and the following orbital parameters: γ=−21±3 km/s and K1=53±3 km/s. The white dwarf is revealed as the system approaches quiescence, which enables us to infer the effective temperature of the primary Teff=11600±400K. The donor temperature is estimated ≲2200K and suggestive of a system approaching the period minimum. Doppler maps in quiescence show the presence of the hot spot in HeI line at the expected accretion disc-stream shock position and an unusual structure of the accretion disc in Hα.

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Statement of the Astronomy research unit

February 24th, 2019 / Comments Off on

Statement of the Astronomy research unit

/ by Vitaly

  

Dear colleagues,

 
The Astronomy research unit of the University of Oulu is the northernmost department of astronomy in the world at a mere one degree south of the Polar Circle. We are a small but scientifically active research group consisting of 4 senior researchers (1 permanent, 3 fixed-term) and externally funded postdocs (3) and PhD students (4). According to all measures, we are proud to count ourselves among the best research units of our university. However, despite our success in attracting external funding (currently in excess of 300k€ per year), a strong publication track record (99 papers in 2016-2018, including 4 in Science and Nature) and a well-developed teaching curriculum, the Astronomy research unit is now in serious danger.
 
Without any preliminary consultations with the staff or the unit leader, the university board has decided to start a process that aims at terminating the main subject status of Astronomy, and converting two of the current astronomy researcher positions to teaching positions in Physics. This would be a serious blow for us, but it is in line with other actions taken previously by the faculty of science against the Astronomy unit, like a series of budget cuts, and the denial by the dean to approve our suggestions for continuation contracts of key personnel of the unit. The loss of the main subject status may sound like a harmless thing. But it is not: the process (called YT-negotiations), initiated by the dean of the faculty of science, is usually used by employers in Finland to terminate work contracts “efficiently” in a situation of economic difficulties. It is a heavy cannon, and it is surprising that this heavy measure is used for this purpose, in particular since the Astronomy unit is producing positive net income to the university, via the bonus university receives from the Ministry of Education and Culture based on the unit’s research output. We are afraid that the process will permit the faculty to take away positions from our unit. This will endanger the unit as a whole, because our budget is directly related to the research output, and a reduction in research staff would lead to a downward spiral and eventual termination of our research unit within a few forthcoming years.
 
The YT-committee will probably support the plans pursued by the faculty. However, the final decision will be made by the rector of the university (prof. Jouko Niinimaki), after discussion with the head of the university board (Dr. Risto Murto). There is no formal way for us to even raise our voice or formulate an appeal against the recommendation by the committee. In this situation, our only hope is the international astronomy community. We hope that supporting statements from international astronomy departments and institutes could be sent directly to the Rector’s office. Of course you cannot directly comment on the quality and quantity of teaching in our unit, having not seen it in person. But if you decide to support us, you could express your worry on the consequences of a reduction in staff on the research output of the unit and the international collaborations. For instance, during the last 2 years our researchers have been awarded 40% of all accepted ESO proposals with a Finland-based PI, with only 15% of the astronomy personnel in Finland. The Finnish investment in ESO is the largest scientific investment for astronomy in the country. Taking away positions from the group in Oulu would significantly decrease the science return for Finland.
 
If you decide to support us or you have any questions, please write me a message at vitaly@neustroev.net and I will then send you the addresses, to which you can send your statement.
 
Thank you for your consideration,
 
Dr. Vitaly Neustroev
on behalf of the members of the Astronomy research unit
 

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First time detection of a GRB at sub-TeV energies: MAGIC detected the GRB 190114C

January 15th, 2019 / Comments Off on First time detection of a GRB at sub-TeV energies: MAGIC detected the GRB 190114C / by Vitaly

After 15 years of dreaming about the GRB detection, tonight it became reality: MAGIC detected a GRB at a red-shift of 0.42 with > 20 sigma in 20 minutes observation time! We have already issued an ATel #12390 on this very hot topic:

The MAGIC telescopes performed a rapid follow-up observation of GRB 190114C (Gropp et al., GCN 23688; Tyurina et al., GCN 23690, de Ugarte Postigo et al., GCN 23692, Lipunov et al. GCN 23693, Selsing et al. GCN 23695). This observation was triggered by the Swift-BAT alert; we started observing at about 50s after Swift T0: 20:57:03.19. The MAGIC real-time analysis shows a significance >20 sigma in the first 20 min of observations (starting at T0+50s) for energies >300GeV. The relatively high detection threshold is due to the large zenith angle of observations (>60 degrees) and the presence of partial Moon. Given the brightness of the event, MAGIC will continue the observation of GRB 190114C until it is observable tonight and also in the next days.

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A press conference announcing astrophysics breakthrough

July 12th, 2018 / Comments Off on A press conference announcing astrophysics breakthrough / by Vitaly

Today there will be a press conference announcing recent multi-messenger astrophysics findings led by the NSF’s IceCube Neutrino Observatory at the South Pole and the MAGIC collaboration. The briefing will feature leading astrophysicists from across the globe.

The multi-messenger press-conference will be directly streamed live to
https://www.youtube.com/c/VideosatNSF/live

Those of you who want to watch the press-conference can connect at
———————
La Palma, Canary Islands: 16:00
CET: 17:00
Finland: 18:00
—————————

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MAGIC celebrates its 15th anniversary!

July 10th, 2018 / Comments Off on MAGIC celebrates its 15th anniversary! / by Vitaly

MAGIC (Major Atmospheric Gamma Imaging Cherenkov) is a system of two 17-m Imaging Atmospheric Cherenkov Telescopes. The MAGIC collaboration consists of about 165 astrophysicists from 24 institutions and consortia from 11 countries. I’m a member of MAGIC since 2013. This year, MAGIC celebrates its 15th anniversary! Our colleagues had produced a nice MAGIC 15th birthday celebration movie. Enjoy!

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Another MAGIC paper accepted by MNRAS

July 6th, 2018 / Comments Off on Another MAGIC paper accepted by MNRAS / by Vitaly

Another MAGIC paper entitled “The broad-band properties of the intermediate synchrotron peaked BL Lac S2 0109+22 from radio to VHE gamma rays” has been accepted for publication in MNRAS:
arXiv:1807.02095

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New MAGIC papers accepted for publication in A&A

July 5th, 2018 / Comments Off on New MAGIC papers accepted for publication in A&A / by Vitaly

Two new papers have been accepted for publication in A&A. Both papers have been sent to ArXiv:

“Gamma-ray flaring activity of NGC 1275 in 2016-2017 measured by MAGIC”:
ArXiv:1806.01559

“Multi-wavelength characterization of the blazar S5~0716+714 during an unprecedented outburst phase”:
ArXiv:1807.00413

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There is a link between the X-ray behaviour and superhump evolution during superoutbursts of WZ Sge-type stars

December 14th, 2017 / Comments Off on There is a link between the X-ray behaviour and superhump evolution during superoutbursts of WZ Sge-type stars / by Vitaly

The second paper on a study of SSS J122221.7−311525, now in X-rays, has been accepted for publication in A&A. It is entitled “Superhumps linked to X-ray emission. The superoutbursts of SSS J122221.7-311525 and GW Lib”.
Preprint: ArXiv:1712.03515.

Neustroev V. V., Page K. L., Kuulkers E., Osborne J. P., Beardmore A. P., Knigge C., Marsh T., Suleimanov V. F., Zharikov S. V.
Abstract:
We present more than 4 years of Swift X-ray observations of the 2013 superoutburst, subsequent decline and quiescence of the WZ Sge-type dwarf nova SSS J122221.7-311525 (SSS122222) from 6 days after discovery. Only a handful of WZ Sge-type dwarf novae have been observed in X-rays, and until recently GW Lib was the only binary of this type with complete coverage of an X-ray light curve throughout a superoutburst. We collected extensive X-ray data of a second such system to understand the extent to which the unexpected properties of GW Lib are common to the WZ Sge class. We analysed the X-ray light curve and compared it with the behaviour of superhumps which were detected in the optical light curve. We also performed spectral analysis of the data. The results were compared with the properties of GW Lib, for which new X-ray observations were also obtained. SSS122222 was variable and around five times brighter in 0.3-10 keV X-rays during the superoutburst than in quiescence, mainly because of a significant strengthening of a high-energy component of the X-ray spectrum. The post-outburst decline of the X-ray flux lasted at least 500 d. The data show no evidence of the expected optically thick boundary layer in the system during the outburst. SSS122222 also exhibited a sudden X-ray flux change in the middle of the superoutburst, which occurred exactly at the time of the superhump stage transition. A similar X-ray behaviour was also detected in GW Lib. This result demonstrates a relationship between the outer disc and the white dwarf boundary layer for the first time, and suggests that models for accretion discs in high mass ratio accreting binaries are currently incomplete. The very long decline to X-ray quiescence is also in strong contrast to the expectation of low viscosity in the disc after outburst.

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A paper on ASASSN-16eg has been published

December 11th, 2017 / Comments Off on A paper on ASASSN-16eg has been published / by Vitaly

A paper entitled “ASASSN-16eg: New candidate for a long-period WZ Sge-type dwarf nova” has been published in PASJ.
Preprint: arXiv:1708.09206.

Abstract:
We report on our photometric observations of the 2016 superoutburst of ASASSN-16eg. This object showed a WZ Sge-type superoutburst with prominent early superhumps with a period of 0.075478(8) d and a post-superoutburst rebrightening. During the superoutburst plateau, it showed ordinary superhumps with a period of 0.077880(3) d and a period derivative of 10.6(1.1) × 10−5 in stage B. The orbital period (Porb), which is almost identical with the period of the early superhumps, is exceptionally long for a WZ Sge-type dwarf nova. The mass ratio (q = M2/M1) estimated from the period of developing (stage A) superhumps is 0.166(2), which is also too large for a WZ Sge-type dwarf nova. This suggests that the 2:1 resonance can be reached in such high-q systems, contrary to our expectation. Such conditions are considered to be achieved if the mass-transfer rate is much lower than those in typical SU UMa-type dwarf novae that have comparable orbital periods to ASASSN-16eg, and a resultant accumulation of a large amount of matter on the disk is realized at the onset of an outburst. We examined other candidates for long-period WZ Sge-type dwarf novae for their supercycles, which are considered to reflect the mass-transfer rate, and found that V1251 Cyg and RZ Leo have longer supercycles than those of other WZ Sge-type dwarf novae. This result indicates that these long-period objects including ASASSN-16eg have a low mass-transfer rate in comparison to other WZ Sge-type dwarf novae.

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