A classical nova occurs when material accreting onto the surface of a white dwarf in a close binary system ignites in a thermonuclear runaway. Complex structures observed in the ejecta at late stages ...could result from interactions with the companion during the common-envelope phase. Alternatively, the explosion could be intrinsically bipolar, resulting from a localized ignition on the surface of the white dwarf or as a consequence of rotational distortion. Studying the structure of novae during the earliest phases is challenging because of the high spatial resolution needed to measure their small sizes. Here we report near-infrared interferometric measurements of the angular size of Nova Delphini 2013, starting one day after the explosion and continuing with extensive time coverage during the first 43 days. Changes in the apparent expansion rate can be explained by an explosion model consisting of an optically thick core surrounded by a diffuse envelope. The optical depth of the ejected material changes as it expands. We detect an ellipticity in the light distribution, suggesting a prolate or bipolar structure that develops as early as the second day. Combining the angular expansion rate with radial velocity measurements, we derive a geometric distance to the nova of 4.54 ± 0.59 kiloparsecs from the Sun.
We present the results of long-baseline optical interferometry observations using the Precision Astronomical Visual Observations (PAVO) beam combiner at the Center for High Angular Resolution ...Astronomy (CHARA) Array to measure the angular sizes of three bright Kepler stars: θ Cygni, and both components of the binary system 16 Cygni. Supporting infrared observations were made with the Michigan Infrared Combiner (MIRC) and Classic beam combiner, also at the CHARA Array. We find limb-darkened angular diameters of 0.753 ± 0.009 mas for θ Cyg, 0.539 ± 0.007 mas for 16 Cyg A and 0.490 ± 0.006 mas for 16 Cyg B. The Kepler Mission has observed these stars with outstanding photometric precision, revealing the presence of solar-like oscillations. Due to the brightness of these stars the oscillations have exceptional signal-to-noise, allowing for detailed study through asteroseismology, and are well constrained by other observations. We have combined our interferometric diameters with Hipparcos parallaxes, spectrophotometric bolometric fluxes and the asteroseismic large frequency separation to measure linear radii (θ Cyg: 1.48 ± 0.02 R, 16 Cyg A: 1.22 ± 0.02 R, 16 Cyg B: 1.12 ± 0.02 R), effective temperatures (θ Cyg: 6749 ± 44 K, 16 Cyg A: 5839 ± 42 K, 16 Cyg B: 5809 ± 39 K) and masses (θ Cyg: 1.37 ± 0.04 M, 16 Cyg A: 1.07 ± 0.05 M, 16 Cyg B: 1.05 ± 0.04 M) for each star with very little model dependence. The measurements presented here will provide strong constraints for future stellar modelling efforts.
Searches are performed for nonresonant and resonant di-Higgs boson production in the b¯bγγ final state. The dataset used corresponds to an integrated luminosity of 139 fb−1 of proton–proton ...collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No excess above the expected background is found and upper limits on the di-Higgs boson production cross sections are set. A 95% confidence-level upper limit of 4.2 times the cross section predicted by the Standard Model is set on pp→HH nonresonant production, where the expected limit is 5.7 times the Standard Model predicted value. The expected constraints are obtained for a background hypothesis excluding pp→HH production. The observed (expected) constraints on the Higgs boson trilinear coupling modifier κλ are determined to be −1.5,6.7 (−2.4,7.7) at 95% confidence level, where the expected constraints on κλ are obtained excluding pp→HH production from the background hypothesis. For resonant production of a new hypothetical scalar particle X (X→HH→b¯bγγ), limits on the cross section for pp→X→HH are presented in the narrow-width approximation as a function of mX in the range 251 GeV≤mX≤1000 GeV. The observed (expected) limits on the cross section for pp→X→HH range from 640 fb to 44 fb (391 fb to 46 fb) over the considered mass range.
Context.
Surface brightness–colour relations (SBCRs) are used to derive the stellar angular diameters from photometric observations. They have various astrophysical applications, such as the distance ...determination of eclipsing binaries or the determination of exoplanet parameters. However, strong discrepancies between the SBCRs still exist in the literature, in particular for early and late-type stars.
Aims.
We aim to calibrate new SBCRs as a function of the spectral type and the luminosity class of the stars. Our goal is also to apply homogeneous criteria to the selection of the reference stars and in view of compiling an exhaustive and up-to-date list of interferometric late-type targets.
Methods.
We implemented criteria to select measurements in the JMMC Measured Diameters Catalog. We then applied additional criteria on the photometric measurements used to build the SBCRs, together with stellar characteristics diagnostics.
Results.
We built SBCRs for F5/K7–II/III, F5/K7–IV/V, M–II/III and M–V stars, with respective rms of
σ
F
V
= 0.0022 mag,
σ
F
V
= 0.0044 mag,
σ
F
V
= 0.0046 mag, and
σ
F
V
= 0.0038 mag. This results in a precision on the angular diameter of 1.0%, 2.0%, 2.1%, and 1.7%, respectively. These relations cover a large
V
−
K
colour range of magnitude, from 1 to 7.5. Our work demonstrates that SBCRs are significantly dependent on the spectral type and the luminosity class of the star. Through a new set of interferometric measurements, we demonstrate the critical importance of the selection criteria proposed for the calibration of SBCR. Finally, using the
Gaia
photometry for our samples, we obtained (
G
−
K
) SBCRs with a precision on the angular diameter between 1.1% and 2.4%.
Conclusions.
By adopting a refined and homogeneous methodology, we show that the spectral type and the class of the star should be considered when applying an SBCR. This is particularly important in the context of PLATO.
Stellar activity observed as large surface spots, radio flares, or emission lines is often found in binary systems. UX Arietis exhibits these signs of activity, originating on the K0 subgiant primary ...component. Our aim is to resolve the binary, measure the orbital motion, and provide accurate stellar parameters such as masses and luminosities to aid in the interpretation of the observed phenomena. Using the CHARA six-telescope optical long-baseline array on Mount Wilson, California, we obtained amplitudes and phases of the interferometric visibility on baselines up to 330 m in length, resolving the two components of the binary. We reanalyzed archival Center for Astrophysics spectra to disentangle the binary component spectra and the spectrum of the third component, which was resolved by speckle interferometry. We also obtained new spectra with the Nordic Optical Telescope, and we present new photometric data that we use to model stellar surface spot locations. Both interferometric visibilities and spectroscopic radial velocities are modeled with a spotted primary stellar surface using the Wilson-Devinney code. We fit the orbital elements to the apparent orbit and radial velocity data to derive the distance (52.1 0.8 pc) and stellar masses ( , ). The radius of the primary can be determined to be and that of the secondary to be . The equivalent spot coverage of the primary component was found to be 62% with an effective temperature 20% below that of the unspotted surface.
A search for heavy resonances decaying into a W or Z boson and a Higgs boson produced in proton − proton collisions at the Large Hadron Collider at √s = 13 TeV is presented. The analysis utilizes the ...dominant W → q¯q′ or Z → q¯q and H → b¯b decays with substructure techniques applied to large-radius jets. A sample corresponding to an integrated luminosity of 139 fb−1 collected with the ATLAS detector is analyzed and no significant excess of data is observed over the background prediction. The results are interpreted in the context of the heavy vector triplet model with spin-1 W′ and Z′ bosons. Upper limits on the cross section are set for resonances with mass between 1.5 and 5.0 TeV, ranging from 6.8 to 0.53 fb for W → WH and from 8.7 to 0.53 fb for Z′ → ZH at the 95% confidence level.
After an 11-year observing campaign, we present the combined visual-spectroscopic orbit of the formerly unremarkable bright star HR 7345 (HD 181655, HIP 94981, GJ 754.2). Using the Separated Fringe ...Packet method with the CHARA Array, we were able to determine a difficult-to-complete orbital period of 331.609 0.004 days. The 11-month period causes the system to be hidden from interferometric view behind the Sun for three years at a time. Due to the high-eccentricity orbit of about 90% of a year, after 2018 January the periastron phase will not be observable again until late 2021. Hindered by its extremely high eccentricity of 0.9322 0.0001, the double-lined spectroscopic phase of HR 7345 is observable for 15 days. Such a high eccentricity for HR 7345 places it among the most eccentric systems in catalogs of both visual and spectroscopic orbits. For this system, we determine nearly identical component masses of 0.941 0.076 M and 0.926 0.075 M as well as an orbital parallax of 41.08 0.77 mas.
We present the first K'-band, long-baseline interferometric observations of the northern Be stars g Cas, h Per, Tau, and Dra. The measurements were made with multiple telescope pairs of the CHARA ...Array interferometer and in every case the observations indicate that the circumstellar disks of the targets are resolved. We fit the interferometric visibilities with predictions from a simple disk model that assumes an isothermal gas in Keplerian rotation. We derive fits of the four model parameters (disk base density, radial density exponent, disk normal inclination, and position angle) for each of the targets. The resulting densities are in broad agreement with prior studies of the IR excess flux, and the resulting orientations generally agree with those from interferometric Ha and continuum polarimetric observations. We find that the angular size of the K' disk emission is smaller than that determined for the Ha emission, and we argue that the difference is the result of a larger Ha opacity and the relatively larger neutral hydrogen fraction with increasing disk radius. All the targets are known binaries with faint companions, and we find that companions appear to influence the interferometric visibilities in the cases of h Per and Dra. We also present contemporaneous observations of the Ha, Hg, and Brg emission lines. Synthetic model profiles of these lines that are based on the same disk inclination and radial density exponent as derived from the CHARA Array observations match the observed emission line strength if the disk base density is reduced by -1.7 dex.
This Letter reports the observation of τ-lepton pair production in ultraperipheral lead-lead collisions, Pb+Pb→Pb(γγ→ττ)Pb, and constraints on the τ-lepton anomalous magnetic moment, aτ. The dataset ...corresponds to an integrated luminosity of 1.44 nb-1 of LHC Pb+Pb collisions at $\sqrt{s_{NN}}$ =5.02 TeV recorded by the ATLAS experiment in 2018. Selected events contain one muon from a τ-lepton decay, an electron or charged-particle track(s) from the other τ-lepton decay, little additional central-detector activity, and no forward neutrons. The γγ→ττ process is observed in Pb+Pb collisions with a significance exceeding 5 standard deviations, and a signal strength of μττ=1.03$^{+0.06}_{-0.05}$ assuming the Standard Model value for aτ. To measure aτ, a template fit to the muon transverse-momentum distribution from τ-lepton candidates is performed, using a dimuon (γγ→μμ) control sample to constrain systematic uncertainties. The observed 95% confidence-level interval for aτ is -0.057 < aτ < 0.024.
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