We present the results of a high-resolution optical spectroscopic study of nine white dwarf candidate members of Praesepe undertaken with the VLT and Ultraviolet and Visual Echelle Spectrograph. We ...find, contrary to a number of previous studies, that WD0836+201 (LB390, EG59) and WD0837+199 (LB393, EG61) are magnetic and non-magnetic white dwarfs, respectively. Subsequently, we determine the radial velocities for the eight non-magnetic degenerates and provide compelling evidence that WD0837+185 is a radial velocity variable and possibly a double-degenerate system. We also find that our result for WD0837+218, in conjunction with its projected spatial location and position in initial mass–final mass space, argues it is more likely to be a field star than a cluster member. After eliminating these two white dwarfs, and WD0836+199 which has no clean Sloan Digital Sky Survey photometry, we use the remaining five stars to substantiate modern theoretical mass–radius relations for white dwarfs. In light of our new results, we re-examine the white dwarf members of Praesepe and use them to further constrain the initial mass–final mass relation (IFMR). We find a near-monotonic IFMR, which can still be adequately represented by simple linear function with only one outlier which may have formed from a blue straggler star.
ABSTRACT
Light curves of the accreting white dwarf pulsator GW Librae spanning a 7.5-month period in 2017 were obtained as part of the Next-Generation Transit Survey. This data set comprises 787 h of ...photometry from 148 clear nights, allowing the behaviour of the long (hours) and short-period (20 min) modulation signals to be tracked from night to night over a much longer observing baseline than has been previously achieved. The long-period modulations intermittently detected in previous observations of GW Lib are found to be a persistent feature, evolving between states with periods ≃ 83 min and 2–4 h on time-scales of several days. The 20 min signal is found to have a broadly stable amplitude and frequency for the duration of the campaign, but the previously noted phase instability is confirmed. Ultraviolet observations obtained with the Cosmic Origin Spectrograph on-board the Hubble Space Telescope constrain the ultraviolet-to-optical flux ratio to ≃5 for the 4 h modulation, and ≲1 for the 20 min period, with caveats introduced by non-simultaneous observations. These results add further observational evidence that these enigmatic signals must originate from the white dwarf, highlighting our continued gap in theoretical understanding of the mechanisms that drive them.
ABSTRACT We present new observations of four closely spaced near-ultraviolet (NUV) transits of the hot Jupiter-like exoplanet WASP-12b using Hubble Space Telescope (HST)/Cosmic Origins Spectrograph ...(COS), significantly increasing the phase resolution of the observed NUV light curve relative to previous observations, while minimizing the temporal variation of the system. We observe significant excess NUV absorption during the transit, with mean normalized in-transit fluxes of , i.e., 2-5 deeper than the optical transit level of for a uniform stellar disk (the exact confidence level depending on the normalization method used). We further observe an asymmetric transit shape, such that the post-conjunction fluxes are overall 2-3 higher than pre-conjunction values, and characterized by rapid variations in count rate between the pre-conjunction and out-of-transit levels. We do not find evidence for an early ingress to the NUV transit as suggested by earlier HST observations. However, we show that the NUV count rate observed prior to the optical transit is highly variable, but overall 2.2-3.0 below the post-transit values and comparable in depth to the optical transit, possibly forming a variable region of NUV absorption from at least phase , limited by the data coverage.
There is a striking and unexplained dearth of brown dwarf companions in close orbits (<3 AU) around stars more massive than the Sun, in stark contrast to the frequency of stellar and planetary ...companions. Although rare and relatively short-lived, these systems leave detectable evolutionary end points in the form of white-dwarf-dwarf binaries and these remnants can offer unique insights into the births and deaths of their parent systems. We present the discovery of a close (orbital separation ~0.006 AU) substellar companion to a massive white dwarf member of the Praesepe star cluster. Using the cluster age and the mass of the white dwarf, we constrain the mass of the white dwarf progenitor star to lie in the range 3.5-3.7 M sub(middot in circle) (B9). The high mass of the white dwarf means the substellar companion must have been engulfed by the B star's envelope while it was on the late asymptotic giant branch (AGB). Hence, the initial separation of the system was ~2 AU, with common envelope evolution reducing the separation to its current value. The initial and final orbital separations allow us to constrain the combination of the common envelope efficiency ( alpha ) and binding energy parameters (lambda) for the AGB star to alpha lambda ~ 3. We examine the various formation scenarios and conclude that the substellar object was most likely captured by the white dwarf progenitor early in the life of the cluster, rather than forming in situ.
This paper presents new observations of the planet-hosting, visual binary GJ 86 (HR 637) using the Hubble Space Telescope. Ultraviolet and optical imaging with WFC3 confirms the stellar companion is ...a degenerate star and indicates the binary semimajor axis is larger than previous estimates, with a 28 au. Optical STIS spectroscopy of the secondary reveals a helium-rich white dwarf with C2 absorption bands and T
eff = 8180 K, thus making the binary system rather similar to Procyon. Based on the 10.8 pc distance, the companion has 0.59 M and descended from a main-sequence A star of 1.9 M with an original orbital separation a 14 au. If the giant planet is coplanar with the binary, the mass of GJ 86Ab is between 4.4 and 4.7 M
Jup.
The similarity of GJ 86 and Procyon prompted a re-analysis of the white dwarf in the latter system, with the tentative conclusion that Procyon hosts a planetesimal population. The periastron distance in Procyon is 20 per cent smaller than in α Cen AB, but the metal-enriched atmosphere of Procyon B indicates that the planet formation process minimally attained 25 km bodies, if not small planets as in α Cen.
This study examines how thermospheric motions due to gravity waves (GWs) drive ion upflow in the F region, modulating the topside ionosphere in a way that can contribute to ion outflow. We present ...incoherent scatter radar data from Sondrestrom, from 31 May 2003 which showed upflow/downflow motions, having a downward phase progression, in the field‐aligned velocity, indicating forcing by a thermospheric GW. The GW‐upflow coupling dynamics are investigated through the use of a coupled atmosphere‐ionosphere model to examine potential impacts on topside ionospheric upflow. Specifically, a sequence of simulations with varying wave amplitude is conducted to determine responses to a range of transient forcing reminiscent of the incoherent scatter radar data. Nonlinear wave effects, resulting from increases in amplitude of the modeled GW, are shown to critically impact the ionospheric response. GW breaking deposits energy into smaller scale wave modes, drives periods of large field‐aligned ion velocities, while also modulating ion densities. Complementary momentum transfer increases the mean flow and, through ion‐neutral drag, can increase ion densities above 300 km. Ionospheric collision frequency (cooling) and photoionization effects (heating), both dependent on ionospheric density, modify the electron temperature; these changes conduct quickly up geomagnetic field lines driving ion upflow at altitudes well above initial disturbances. This flow alters ion populations available for high‐altitude acceleration processes that may lead to outflow into the magnetosphere. We have included a representative source of transverse wave heating which, when supplemented by our GWs, illustrates strengthened upward fluxes in the topside ionosphere.
Key Points
High‐latitude ionospheric upflow can be modulated by thermospheric gravity waves
F region density perturbations due to gravity wave modulations, through heating and cooling processes, modulate the electron temperature
Increases in electron temperature quickly conduct up the magnetic field lines and drive upflow at altitudes above the initial heating region
Context.
Long-period transiting planets provide the opportunity to better understand the formation and evolution of planetary systems. Their atmospheric properties remain largely unaltered by tidal ...or radiative effects of the host star, and their orbital arrangement reflects a different and less extreme migrational history compared to close-in objects. The sample of long-period exoplanets with well-determined masses and radii is still limited, but a growing number of long-period objects reveal themselves in the Transiting Exoplanet Survey Satellite (TESS) data.
Aims.
Our goal is to vet and confirm single-transit planet candidates detected in the TESS space-based photometric data through spectroscopic and photometric follow-up observations with ground-based instruments.
Methods.
We used high-resolution spectrographs to confirm the planetary nature of the transiting candidates and measure their masses. We also used the Next Generation Transit Survey (NGTS) to photometrically monitor the candidates in order to observe additional transits. Using a joint modeling of the light curves and radial velocities, we computed the orbital parameters of the system and were able to precisely measure the mass and radius of the transiting planets.
Results.
We report the discovery of two massive, warm Jupiter-size planets, one orbiting the F8-type star TOI-5153 and the other orbiting the G1-type star NGTS-20 (=TOI-5152). From our spectroscopic analysis, both stars are metal rich with a metallicity of 0.12 and 0.15, respectively. Only TOI-5153 presents a second transit in the TESS extended mission data, but NGTS observed NGTS-20 as part of its mono-transit follow-up program and detected two additional transits. Follow-up high-resolution spectroscopic observations were carried out with CORALIE, CHIRON, FEROS, and HARPS. TOI-5153 hosts a planet with a period of 20.33 days, a planetary mass of 3.26
−0.17
+0.18
Jupiter masses (
M
J
), a radius of 1.06
−0.04
+0.04
R
J
, and an orbital eccentricity of 0.091
−0.026
+0.024
. NGTS-20 b is a 2.98
−0.15
+0.16
M
J
planet with a radius of 1.07
−0.04
+0.04
R
J
on an eccentric 0.432
−0.023
+0.023
orbit with an orbital period of 54.19 days. Both planets are metal enriched and their heavy element content is in line with the previously reported mass-metallicity relation for gas giants.
Conclusions.
Both warm Jupiters orbit moderately bright host stars, making these objects valuable targets for follow-up studies of the planetary atmosphere and measurement of the spin-orbit angle of the system.
A number of ultracool dwarfs emit circularly polarized radio waves generated by the electron cyclotron maser instability. In the solar system such radio is emitted from regions of strong auroral ...magnetic-field-aligned currents. We thus apply ideas developed for Jupiter's magnetosphere, being a well-studied rotationally dominated analog in our solar system, to the case of fast-rotating UCDs. We explain the properties of the radio emission from UCDs by showing that it would arise from the electric currents resulting from an angular velocity shear in the fast-rotating magnetic field and plasma, i.e., by an extremely powerful analog of the process that causes Jupiter's auroras. Such a velocity gradient indicates that these bodies interact significantly with their space environment, resulting in intense auroral emissions. These results strongly suggest that auroras occur on bodies outside our solar system.
Three short-period Jupiters from TESS Nielsen, L. D.; Brahm, R.; Bouchy, F. ...
Astronomy and astrophysics (Berlin),
07/2020, Letnik:
639
Journal Article, Web Resource
Recenzirano
Odprti dostop
We report the confirmation and mass determination of three hot Jupiters discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HIP 65Ab (TOI-129, TIC-201248411) is an ...ultra-short-period Jupiter orbiting a bright (
V
= 11.1 mag) K4-dwarf every 0.98 days. It is a massive 3.213 ± 0.078
M
J
planet in a grazing transit configuration with an impact parameter of
b
= 1.17
−0.08
+0.10
. As a result the radius is poorly constrained, 2.03
−0.49
+0.61
R
J
. The planet’s distance to its host star is less than twice the separation at which it would be destroyed by Roche lobe overflow. It is expected to spiral into HIP 65A on a timescale ranging from 80 Myr to a few gigayears, assuming a reduced tidal dissipation quality factor of
Q
s
′
= 10
7
− 10
9
. We performed a full phase-curve analysis of the TESS data and detected both illumination- and ellipsoidal variations as well as Doppler boosting. HIP 65A is part of a binary stellar system, with HIP 65B separated by 269 AU (3.95 arcsec on sky). TOI-157b (TIC 140691463) is a typical hot Jupiter with a mass of 1.18 ± 0.13
M
J
and a radius of 1.29 ± 0.02
R
J
. It has a period of 2.08 days, which corresponds to a separation of just 0.03 AU. This makes TOI-157 an interesting system, as the host star is an evolved G9 sub-giant star (
V
= 12.7). TOI-169b (TIC 183120439) is a bloated Jupiter orbiting a
V
= 12.4 G-type star. It has a mass of 0.79 ±0.06
M
J
and a radius of 1.09
−0.05
+0.08
R
J
. Despite having the longest orbital period (
P
= 2.26 days) of the three planets, TOI-169b receives the most irradiation and is situated on the edge of the Neptune desert. All three host stars are metal rich with Fe / H ranging from 0.18 to0.24.
We present the results of a photometric and spectroscopic study of the white dwarf candidate members of the intermediate age open clusters NGC 3532 and NGC 2287. Of the nine objects investigated, it ...is determined that six are probable members of the clusters, four in NGC 3532 and two in NGC 2287. For these six white dwarfs, we use our estimates of their cooling times together with the cluster ages to constrain the lifetimes and masses of their progenitor stars. We examine the location of these objects in initial mass–final mass space and find that they now provide no evidence for substantial scatter in initial mass–final mass relation (IFMR) as suggested by previous investigations. Instead, we demonstrate that, when combined with current data from other solar metallicity open clusters and the Sirius binary system, they hint at an IFMR that is steeper in the initial mass range 3 M⊙≲Minit≲ 4 M⊙ than at progenitor masses immediately lower and higher than this. This form is generally consistent with the predictions of stellar evolutionary models and can aid population synthesis models in reproducing the relatively sharp drop observed at the high mass end of the main peak in the mass distribution of white dwarfs.
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