31 research outputs found
Extremely precise age and metallicity of the open cluster NGC 2506 using detached eclipsing binaries
Accurate stellar parameters of stars in open clusters can help constrain models of stellar structure and evolution. Here, we wish to determine the age and metallicity content of the open cluster NGC 2506. To this end, we investigated three detached eclipsing binaries (DEBs; V2032, V4, and V5) for which we determined their masses and radii, as well as four red giant branch stars for which we determined their effective temperatures, surface gravities, and metallicities. Three of the stars in the DEBs have masses close to the cluster turn-off mass, allowing for extremely precise age determination. Comparing the values for the masses and radii of the binaries to BaSTI (a Bag of Stellar Tracks and Isochrones) isochrones, we estimated a cluster age of 2.01 ± 0.10 Gyr. This does depend on the models used in the comparison, where we have found that the inclusion of convective core-overshooting is necessary to properly model the cluster. From red giant branch stars, we determined values for the effective temperatures, the surface gravities, and the metallicities. From these we find a cluster metallicity of â0.36 ± 0.10 dex. Using this value and the values for the effective temperatures, we determine the reddening to be E(b â y) = 0.057 ± 0.004 mag. Furthermore, we derived the distance to the cluster from Gaia parallaxes and found 3.101 ± 0.017 kpc, and we have performed a radial velocity membership determination for stars in the field of the cluster. Finally, we report on the detection of oscillation signals in Îł Dor and ÎŽ Scuti members in data from the Transiting Exoplanet Survey Satellite (TESS) mission, including the possible detection of solar-like oscillations in two of the red giants.Funding for the Stellar
Astrophysics Centre is provided by The Danish National Research
Foundation (Grant agreement no.: DNRF106). ELS gratefully acknowledges support from the (U.S.) National Science Foundation
under grant AST 1817217. This work has made use of data from
the European Space Agency (ESA) mission Gaia (https://www.
cosmos.esa.int/gaia), processed by the Gaia Data Processing and
Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gai
a/dpac/consortium). Funding for the DPAC has been provided by
national institutions, in particular the institutions participating in
the Gaia Multilateral Agreement. This research has made use of
the VizieR catalogue access tool, CDS, Strasbourg, France
The low density, hot Jupiter TOI-640 b is on a polar orbit
TOI-640 b is a hot, puffy Jupiter with a mass of M
and radius of R, orbiting a slightly evolved F-type
star with a separation of R. Through
spectroscopic in-transit observations made with the HARPS spectrograph, we
measured the Rossiter-McLaughlin effect, analysing both in-transit radial
velocities and the distortion of the stellar spectral lines. From these
observations, we find the host star to have a projected obliquity of
. From the TESS light curve, we measured the stellar
rotation period, allowing us to determine the stellar inclination,
, meaning we are viewing the star pole-on. Combining
this with the orbital inclination allowed us to calculate the host star
obliquity, . TOI-640 b joins a group of planets orbiting
over stellar poles within the range . The origin of this
orbital configuration is not well understood.Comment: 15 pages, 12 figures, accepted for publication in A&A, in pres
Refining the prediction for OJ 287 next impact flare arrival epoch
The bright blazar OJ~287 routinely parades high brightness bremsstrahlung
flares which are explained as being a result of a secondary supermassive black
hole (SMBH) impacting the accretion disk of a primary SMBH in a binary system.
We begin by showing that these flares occur at times predicted by a simple
analytical formula, based on the Kepler equation, which explains flares since
1888. The next impact flare, namely the flare number 26, is rather peculiar as
it breaks the typical pattern of two impact flares per 12 year cycle. This will
be the third bremsstrahlung flare of the current cycle that follows the already
observed 2015 and 2019 impact flares from OJ~287. Unfortunately, astrophysical
considerations make it difficult to predict the exact arrival epoch of the
flare number 26. In the second part of the paper, we describe our recent OJ~287
observations. They show that the pre-flare light curve of flare number 22,
observed in 2005, exhibits similar activity as the pre-flare light curve in
2022, preceding the expected flare number 26 in our model. We argue that the
pre-flare activity most likely arises in the primary jet whose activity is
modulated by the transit of the secondary SMBH through the accretion disk of
the primary. Observing the next impact flare of OJ~287 in October 2022 will
substantiate the theory of disk impacts in binary black hole systems.Comment: 16 pages, 2 figure
Refining the 2022 OJ 287 impact flare arrival epoch
The bright blazar OJ~287 routinely parades high brightness bremsstrahlung
flares, which are explained as being a result of a secondary supermassive black
hole (SMBH) impacting the accretion disc of a more massive primary SMBH in a
binary system. The accretion disc is not rigid but rather bends in a calculable
way due to the tidal influence of the secondary. Below we refer to this
phenomenon as a variable disc level. We begin by showing that these flares
occur at times predicted by a simple analytical formula, based on general
relativity inspired modified Kepler equation, which explains impact flares
since 1888.
The 2022 impact flare, namely flare number 26, is rather peculiar as it
breaks the typical pattern of two impact flares per 12-year cycle. This is the
third bremsstrahlung flare of the current cycle that follows the already
observed 2015 and 2019 impact flares from OJ~287.
It turns out that the arrival epoch of flare number 26 is sensitive to the
level of primary SMBH's accretion disc relative to its mean level in our model.
We incorporate these tidally induced changes in the level of the accretion disc
to infer that the thermal flare should have occurred during July-August 2022,
when it was not possible to observe it from the Earth. Thereafter, we explore
possible observational evidence for certain pre-flare activity by employing
spectral and polarimetric data from our campaigns in 2004/05 and 2021/22. We
point out theoretical and observational implications of two observed
mini-flares during January-February 2022.Comment: 29 pages, 6 figures, 1 table. arXiv admin note: text overlap with
arXiv:2209.0836
On the need of an ultramassive black hole in OJ 287
The highly variable blazar OJ~287 is commonly discussed as an example of a
binary black hole system. The 130 year long optical light curve is well
explained by a model where the central body is a massive black hole of
18.3510 solar mass that supports a thin accretion disc. The
secondary black hole of 0.1510 solar mass impacts the disc twice
during its 12 year orbit, and causes observable flares. Recently, it has been
argued that an accretion disc with a typical AGN accretion rate and above
mentioned central body mass should be at least six magnitudes brighter than
OJ~287's host galaxy and would therefore be observationally excluded. Based on
the observations of OJ~287's radio jet, detailed in Marscher and Jorstad
(2011), and up-to-date accretion disc models of Azadi et al. (2022), we show
that the V-band magnitude of the accretion disc is unlikely to exceed the host
galaxy brightness by more than one magnitude, and could well be fainter than
the host. This is because accretion power is necessary to launch the jet as
well as to create electromagnetic radiation, distributed across many
wavelengths, and not concentrated especially on the optical V-band. Further, we
note that the claimed V-band concentration of accretion power leads to serious
problems while interpreting observations of other Active Galactic Nuclei.
Therefore, we infer that the mass of the primary black hole and its accretion
rate do not need to be smaller than what is determined in the standard model
for OJ~287
The Transiting Multi-planet System HD15337: Two Nearly Equal-mass Planets Straddling the Radius Gap
We report the discovery of a super-Earth and a sub-Neptune transiting the star HD 15337 (TOI-402, TIC 120896927), a bright (V = 9) K1 dwarf observed by the Transiting Exoplanet Survey Satellite (TESS) in Sectors 3 and 4. We combine the TESS photometry with archival High Accuracy Radial velocity Planet Searcher spectra to confirm the planetary nature of the transit signals and derive the masses of the two transiting planets. With an orbital period of 4.8 days, a mass of and a radius of 1.64 ± 0.06 R â, HD 15337 b joins the growing group of short-period super-Earths known to have a rocky terrestrial composition. The sub-Neptune HD 15337 c has an orbital period of 17.2 days, a mass of , and a radius of 2.39 ± 0.12 R â, suggesting that the planet might be surrounded by a thick atmospheric envelope. The two planets have similar masses and lie on opposite sides of the radius gap, and are thus an excellent testbed for planet formation and evolution theories. Assuming that HD 15337 c hosts a hydrogen-dominated envelope, we employ a recently developed planet atmospheric evolution algorithm in a Bayesian framework to estimate the history of the high-energy (extreme ultraviolet and X-ray) emission of the host star. We find that at an age of 150 Myr, the star possessed on average between 3.7 and 127 times the high-energy luminosity of the current Sun
Observational Implications of OJ 287âs Predicted 2022 Disk Impact in the Black Hole Binary Model
We present a summary of the results of the OJ 287 observational campaign, which was carried out during the 2021/2022 observational season. This season is special in the binary model because the major axis of the precessing binary happens to lie almost exactly in the plane of the accretion disc of the primary. This leads to pairs of almost identical impacts between the secondary black hole and the accretion disk in 2005 and 2022. In 2005, a special flare called âblue flashâ was observed 35 days after the disk impact, which should have also been verifiable in 2022. We did observe a similar flash and were able to obtain more details of its properties. We describe this in the framework of expanding cloud models. In addition, we were able to identify the flare arising exactly at the time of the disc crossing from its photo-polarimetric and gamma-ray properties. This is an important identification, as it directly confirms the orbit model. Moreover, we saw a huge flare that lasted only one day. We may understand this as the lighting up of the jet of the secondary black hole when its Roche lobe is suddenly flooded by the gas from the primary disk. Therefore, this may be the first time we directly observed the secondary black hole in the OJ 287 binary system
Greening of the brown-dwarf desert EPIC 212036875b: a 51 M-J object in a 5-day orbit around an F7V star
Context. Although more than 2000 brown dwarfs have been detected to date, mainly from direct imaging, their characterisation is difficult due to their faintness and model-dependent results. In the case of transiting brown dwarfs, however, it is possible to make direct high-precision observations. Aims. Our aim is to investigate the nature and formation of brown dwarfs by adding a new well-characterised object, in terms of its mass, radius and bulk density, to the currently small sample of less than 20 transiting brown dwarfs. Methods. One brown dwarf candidate was found by the KESPRINT consortium when searching for exoplanets in the K2 space mission Campaign 16 field. We combined the K2 photometric data with a series of multicolour photometric observations, imaging, and radial velocity measurements to rule out false positive scenarios and to determine the fundamental properties of the system. Results. We report the discovery and characterisation of a transiting brown dwarf in a 5.17-day eccentric orbit around the slightly evolved F7V star EPIC 212036875. We find a stellar mass of 1.15 +/- 0.08 M-circle dot, a stellar radius of 1.41 +/- 0.05 R-circle dot, and an age of 5.1 +/- 0.9 Gyr. The mass and radius of the companion brown dwarf are 51 +/- 2 M-J and 0.83 +/- 0.03 R-J, respectively, corresponding to a mean density of 108(-13)(+15) g cm(-3). Conclusions. EPIC 212036875 b is a rare object that resides in the brown-dwarf desert. In the mass-density diagram for planets, brown dwarfs, and stars, we find that all giant planets and brown dwarfs follow the same trend from similar to 0.3 M-J to the turn-over to hydrogen burning stars at similar to 73 M-J. EPIC 212036875 b falls close to the theoretical model for mature H/He dominated objects in this diagram as determined by interior structure models. We argue that EPIC 212036875 b formed via gravitational disc instabilities in the outer part of the disc, followed by a quick migration. Orbital tidal circularisation may have started early in its history for a brief period when the brown dwarf\u27s radius was larger. The lack of spin-orbit synchronisation points to a weak stellar dissipation parameter (Q(star)\u27 greater than or similar to 10(8)), which implies a circularisation timescale of greater than or similar to 23 Gyr, or suggests an interaction between the magnetic and tidal forces of the star and the brown dwarf