Tests of Einstein's general theory of relativity have mostly been carried out in weak gravitational fields where the space-time curvature effects are first-order deviations from Newton's theory. ...Binary pulsars provide a means of probing the strong gravitational field around a neutron star, but strong-field effects may be best tested in systems containing black holes. Here we report such a test in a close binary system of two candidate black holes in the quasar OJ 287. This quasar shows quasi-periodic optical outbursts at 12-year intervals, with two outburst peaks per interval. The latest outburst occurred in September 2007, within a day of the time predicted by the binary black-hole model and general relativity. The observations confirm the binary nature of the system and also provide evidence for the loss of orbital energy in agreement (within 10 per cent) with the emission of gravitational waves from the system. In the absence of gravitational wave emission the outburst would have happened 20 days later.
ABSTRACT
This paper presents the results of a combined spectroscopic and photometric study of 20 contact binary systems: HV Aqr, OO Aql, FI Boo, TX Cnc, OT Cnc, EE Cet, RW Com, KR Com, V401 Cyg, ...V345 Gem, AK Her, V502 Oph, V566 Oph, V2612 Oph, V1363 Ori, V351 Peg, V357 Peg, Y Sex, V1123 Tau, and W UMa, which was conducted in the frame of the W UMa Project. Together with 51 already covered by the project and an additional 67 in the existing literature, these systems bring the total number of contact binaries with known combined spectroscopic and photometric solutions to 138. It was found that mass, radius, and luminosity of the components follow certain relations along the MS and new empirical power relations are extracted. We found that 30 per cent of the systems in the current sample show extreme values in their parameters, expressed in their mass ratio or fill-out factor. This study shows that, among the contact binary systems studied, some have an extremely low mass ratio (q < 0.1) or an ultrashort orbital period (Porb < 0.25 d), which are expected to show evidence of mass transfer progress. The evolutionary status of these components is discussed with the aid of correlation diagrams and their physical and orbital parameters compared to those in the entire sample of known contact binaries. The existence of very short orbital periods confirms the very slow nature of the merging process, which seems to explain why their components still exist as MS stars in contact configurations even after several Gyr of evolution.
The evolution of young stars and disks is driven by the interplay of several processes, notably the accretion and ejection of material. These processes, critical to correctly describe the conditions ...of planet formation, are best probed spectroscopically. Between 2020 and 2022, about 500orbits of the
Hubble
Space Telescope (HST) are being devoted in to the ULLYSES public survey of about 70 low-mass (
M
⋆
≤ 2
M
⊙
) young (age < 10 Myr) stars at UV wavelengths. Here, we present the PENELLOPE Large Program carried out with the ESO Very Large Telescope (VLT) with the aim of acquiring, contemporaneously to the HST, optical ESPRESSO/UVES high-resolution spectra for the purpose of investigating the kinematics of the emitting gas, along with UV-to-NIR X-shooter medium-resolution flux-calibrated spectra to provide the fundamental parameters that HST data alone cannot provide, such as extinction and stellar properties. The data obtained by PENELLOPE have no proprietary time and the fully reduced spectra are being made available to the whole community. Here, we describe the data and the first scientific analysis of the accretion properties for the sample of 13 targets located in the Orion OB1 association and in the
σ
-Orionis cluster, observed in November–December 2020. We find that the accretion rates are in line with those observed previously in similarly young star-forming regions, with a variability on a timescale of days (≲3). The comparison of the fits to the continuum excess emission obtained with a slab model on the X-shooter spectra and the HST/STIS spectra shows a shortcoming in the X-shooter estimates of ≲10%, which is well within the assumed uncertainty. Its origin can be either due to an erroneous UV extinction curve or to the simplicity of the modeling and, thus, this question will form the basis of the investigation undertaken over the course of the PENELLOPE program. The combined ULLYSES and PENELLOPE data will be key in attaining a better understanding of the accretion and ejection mechanisms in young stars.
We present results of the modelling of multicolour light curves of 10 contact binary systems: V376 And, V523 Cas, CC Com, BX Dra, FG Hya, UZ Leo, XY Leo, AM Leo, EX Leo and RT LMi. The solutions ...resulted in a contact configuration for all systems. We found only FG Hya and UZ Leo to be in deep contact, the latter almost filling the outer critical lobe. The absolute parameters of the components have been determined with an accuracy of about a few per cent based on combined photometric and radial velocity curves, enlarging the sample of systems to 58 for which the physical parameters have been obtained in a uniform way. All but three systems (BX Dra, AM Leo and RT LMi) show asymmetries and peculiarities in the observed light curves, interpreted as resulting from their magnetic activity.
PENELLOPE Frasca, A.; Boffin, H. M. J.; Manara, C. F. ...
Astronomy and astrophysics (Berlin),
12/2021, Letnik:
656
Journal Article
Recenzirano
Odprti dostop
We present the results of our study of the close pre-main sequence spectroscopic binary CVSO 104 in Ori OB1, based on data obtained within the PENELLOPE legacy program. We derive, for the first time, ...the orbital elements of the system and the stellar parameters of the two components. The system is composed of two early M-type stars and has an orbital period of about five days and a mass ratio of 0.92, but contrary to expectations, it does not appear to have a tertiary companion. Both components have been (quasi-)synchronized, but the orbit is still very eccentric. The spectral energy distribution clearly displays a significant infrared excess that is compatible with a circumbinary disk. The analysis of He
I
and Balmer line profiles, after the removal of the composite photospheric spectrum, reveals that both components are accreting at a similar level. We also observe excess emission in H
α
and H
β
, which appears redshifted or blueshifted by more than 100 km s
−1
with respect to the mass center of the system, depending on the orbital phase. This additional emission could be connected with accretion structures, such as funnels of matter from the circumbinary disk. We also analyze the optical companion located at about 2.″4 from the spectroscopic binary. This companion, which we named CVSO 104 B, turns out to be a background Sun-like star that is not physically associated with the PMS system and does not belong to Ori OB1.
Context.
EX Lupi is the prototype by which EXor-type outbursts have been defined. It has experienced multiple accretion-related bursts and outbursts throughout the past decades, and the study of ...these events has greatly extended our knowledge about their effects. Notably, this star experienced a new burst in 2022.
Aims.
We aim to investigate whether the recent brightening was caused by temporarily increased accretion or by a brief decrease in the extinction and study the evolution of the EX Lupi system throughout this event.
Methods.
We used multi-band photometry to create color-color and color-magnitude diagrams to exclude the possibility that the brightening could be explained by a decrease in extinction. We obtained spectra using the X-shooter instrument of the Very Large Telescope (VLT) to determine the
L
acc
and
Ṁ
acc
during the peak of the burst and after its return to quiescence using two different methods: empirical relationships between line luminosity and
L
acc
, and a slab model of the whole spectrum. We examined the 130-yr light curve of EX Lupi to provide statistics on the number of outbursts experienced during this period of time.
Results.
Our analysis of the data taken during the 2022 burst confirmed that a change in extinction is not responsible for the brightening. Our two approaches in calculating the
Ṁ
acc
were in agreement and resulted in values that are two orders of magnitude above what had previously been estimated for EX Lupi using only a couple of individual emission lines, thus suggesting that EX Lupi is a strong accretor even when in quiescence. We determined that in 2022 March, the
Ṁ
acc
increased by a factor of seven with respect to the quiescent level. We also found hints that even though the
Ṁ
acc
had returned to near pre-outburst levels, certain physical properties of the gas (i.e., temperature and density) had not returned to the quiescent values.
Conclusions.
We found that the mass accreted during this three-month event was 0.8 lunar masses, which is approximately half of what is accreted during a year of quiescence. We calculated that if EX Lupi remains as active as it has been for the past 130 yr, during which it has experienced at least three outbursts and ten bursts, then it will deplete the mass of its circumstellar material in less than 160 000 yr.
The blazar OJ 287 has produced two major optical outburst events during the years 2005-2008. These are the latest in a series of outbursts that have occurred repeatedly at 12 year intervals since ...early 1900s. It has been possible to explain the historical light curve fairly well by using a binary black hole model where the secondary black hole impacts the accretion disk of the primary twice during the 12 year orbital cycle. We will ask here how well does the latest light-curve fit with this model. We use a 10 million particle disk to model the accretion disk of the primary black hole. The rate of transfer of particles through the 10 Schwarzschild radius cylinder around the primary is followed. The secondary induces an inward flow through this surface. The inward flow rate is compared with the historical light curve as well as with the most recent observations reported in this paper. The observations have been carried out by using a number of small and medium size telescopes in different locations in order to ensure a dense light-curve coverage. The 'inflow light curve' and the optical light curve of OJ 287 have a close resemblance to each other. It suggests that the tidally induced accretion flow is responsible for the main features of the optical light curve, with the exception of the quasi-periodic double peaks. It implies a close connection between the accretion disk and the jet where the optical synchrotron emission is presumably generated.
ABSTRACT OJ 287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts that are predictable in a binary black hole model. The model predicted a major optical ...outburst in 2015 December. We found that the outburst did occur within the expected time range, peaking on 2015 December 5 at magnitude 12.9 in the optical R-band. Based on Swift/XRT satellite measurements and optical polarization data, we find that it included a major thermal component. Its timing provides an accurate estimate for the spin of the primary black hole, . The present outburst also confirms the established general relativistic properties of the system such as the loss of orbital energy to gravitational radiation at the 2% accuracy level, and it opens up the possibility of testing the black hole no-hair theorem with 10% accuracy during the present decade.
Gaia18cjb is one of the Gaia -alerted eruptive young star candidates that has been experiencing a slow and strong brightening during the last 13 years, similarly to some FU Orionis-type objects. The ...aim of this work is to derive the young stellar nature of Gaia18cjb and determine its physical and accretion properties to classify its variability. We conducted monitoring observations using multi-filter optical and near-infrared (NIR) photometry, as well as NIR spectroscopy.
We present an analysis of pre-outburst and outburst optical and IR light curves, color-magnitude diagrams in different bands, the detection of NIR spectral lines, and estimates of both stellar and accretion parameters during the burst. The optical light curve shows an unusually long (over 8 years) brightening event of 5\,mag in the last 13 years, before reaching a plateau indicating that the burst is still ongoing, suggesting a FU\,Orionis-like (FUor-like) nature. The same outburst is less strong in the IR light curves. The NIR spectra, obtained during the outburst, exhibit emission lines typical of highly accreting low-intermediate mass young stars with typical EX\,Lupi-type (EXor) features. The spectral index of Gaia18cjb SED classifies it as a Class I in the pre-burst stage and a flat-spectrum young stellar object (YSO) during the burst. Gaia18cjb is an eruptive YSO that exhibits FUor-like photometric features (in terms of brightening amplitude and length of the burst) as well as EXor-like spectroscopic features and accretion rate. Its nature appears similar to that of V350\,Cep and V1647\,Ori, which have been classified as objects in between FUors and EXors.
We present the results of a multisite photometric campaign on the pulsating B-type hot subdwarf star Balloon 090100001 (Bal09). The star is one of the two known hybrid hot subdwarfs with both long- ...and short-period oscillations, theoretically attributed to g and p modes. The campaign involved eight telescopes with three obtaining UBVR data, four B-band data and one Strömgren uvby photometry. The campaign covered 48 nights, providing a temporal resolution of 0.36 μHz with a detection threshold of about 0.2 mmag in B-filter data. Bal09 has the richest pulsation spectrum of any known pulsating subdwarf B star, and our analysis detected 114 frequencies including 97 independent and 17 combination ones. Most of the 24 g-mode frequencies are between 0.1 and 0.4 mHz. Of the remaining 73, presumably p modes, 72 group into four distinct regions near 2.8, 3.8, 4.7 and 5.5 mHz. The density of frequencies requires that some modes must have degrees ℓ larger than 2. The modes in the 2.8 mHz region have the largest amplitudes. The strongest mode (f1) is most likely radial, while the remaining ones in this region form two nearly symmetric multiplets: a triplet and quintuplet, attributed to rotationally split ℓ= 1 and 2 modes, respectively. We find clear increases of splitting in both multiplets between the 2004 and 2005 observing campaigns, amounting to ∼15 per cent on average. The observed splittings imply that the rotational rate in Bal09 depends on stellar latitude and is the fastest on the equator. We also speculate on the possible reasons for the changes of splitting. The only plausible explanation we find is torsional oscillation. This hypothesis, however, needs to be verified in the future by detailed modelling. In this context, it is very important to monitor the splittings on a longer time-scale as their behaviour may help to explain this interesting phenomenon. The amplitudes of almost all terms detected in both 2004 and 2005 were found to vary. This is evident even during one season; for example, amplitudes of modes f8 and fC were found to change by a factor of 2–3 within about 50 d during 2005. We use a small grid of models to constrain the main mode (f1), which most likely represents the radial fundamental pulsation. The groups of p-mode frequencies appear to lie in the vicinity of the consecutive radial overtones, up to the third one. Despite the large number of g-mode frequencies observed, we failed to identify them, most likely because of the disruption of asymptotic behaviour by mode trapping. The observed frequencies were not, however, fully exploited in terms of seismic analysis which should be done in the future with a larger grid of reliable evolutionary models of hot subdwarfs.
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