More Like this

1. The Directly Imaged Exoplanet Host Star 51 Eridani is a Gamma Doradus Pulsator

   https://doi.org/10.3847/1538-4357/ac9229  

   Sepulveda, Aldo G. ; Huber, Daniel ; Zhang, Zhoujian ; Li, Gang ; Liu, Michael C. ; Bedding, Timothy R. ( October 2022 , The Astrophysical Journal)

   51 Eri is well known for hosting a directly imaged giant planet and for its membership to theβPictoris moving group. Using 2 minute cadence photometry from the Transiting Exoplanet Survey Satellite (TESS), we detect multiperiodic variability in 51 Eri that is consistent with pulsations of Gamma Doradus (γDor) stars. We identify the most significant pulsation modes (with frequencies between ∼0.5 and 3.9 cycles day⁻¹and amplitudes ranging between ∼1 and 2 mmag) as dipole and quadrupole gravity modes, as well as Rossby modes, as previously observed in KeplerγDor stars. Our results demonstrate that previously reported variability attributed to stellar rotation is instead likely due toγDor pulsations. Using the mean frequency of theℓ= 1 gravity modes, together with empirical trends of the KeplerγDor population, we estimate a plausible stellar core rotation period of${0.9}_{-0.1}^{+0.3}$days for 51 Eri. We find no significant evidence for transiting companions around 51 Eri in the residual light curve. The detection ofγDor pulsations presented here, together with follow-up observations and modeling, may enable the determination of an asteroseismic age for this benchmark system. Future TESS observations would allow a constraint on the stellar core rotation rate, which in turn traces the surface rotation rate, andmore »thus would help clarify whether or not the stellar equatorial plane and orbit of 51 Eri b are coplanar.

   « less
2. TESS first look at evolved compact pulsators: Asteroseismology of the pulsating helium-atmosphere white dwarf TIC 257459955

   https://doi.org/10.1051/0004-6361/201936340  

   Bell, Keaton J. ; Córsico, Alejandro H. ; Bischoff-Kim, Agnès ; Althaus, Leandro G. ; Bradley, Paul A. ; Calcaferro, Leila M. ; Montgomery, Michael H. ; Uzundag, Murat ; Baran, Andrzej S. ; Bognár, Zsófia ; et al ( December 2019 , Astronomy & Astrophysics)

   Context. Pulsation frequencies reveal the interior structures of white dwarf stars, shedding light on the properties of these compact objects that represent the final evolutionary stage of most stars. Two-minute cadence photometry from the Transiting Exoplanet Survey Satellite (TESS) records pulsation signatures from bright white dwarfs over the entire sky. Aims. As part of a series of first-light papers from TESS Asteroseismic Science Consortium Working Group 8, we aim to demonstrate the sensitivity of TESS data, by measuring pulsations of helium-atmosphere white dwarfs in the DBV instability strip, and what asteroseismic analysis of these measurements can reveal about their stellar structures. We present a case study of the pulsating DBV WD 0158−160 that was observed as TIC 257459955 with the two-minute cadence for 20.3 days in TESS Sector 3. Methods. We measured the frequencies of variability of TIC 257459955 with an iterative periodogram and prewhitening procedure. The measured frequencies were compared to calculations from two sets of white dwarf models to constrain the stellar parameters: the fully evolutionary models from LPCODE and the structural models from WDEC . Results. We detected and measured the frequencies of nine pulsation modes and eleven combination frequencies of WD 0158−160 to ∼0.01  μ Hzmore »precision. Most, if not all, of the observed pulsations belong to an incomplete sequence of dipole (ℓ = 1) modes with a mean period spacing of 38.1 ± 1.0 s. The global best-fit seismic models from both LPCODE and WDEC have effective temperatures that are ≳3000 K hotter than archival spectroscopic values of 24 100–25 500 K; however, cooler secondary solutions are found that are consistent with both the spectroscopic effective temperature and distance constraints from Gaia astrometry. Conclusions. Our results demonstrate the value of the TESS data for DBV white dwarf asteroseismology. The extent of the short-cadence photometry enables reliably accurate and extremely precise pulsation frequency measurements. Similar subsets of both the LPCODE and WDEC models show good agreement with these measurements, supporting that the asteroseismic interpretation of DBV observations from TESS is not dominated by the set of models used. However, given the sensitivity of the observed set of pulsation modes to the stellar structure, external constraints from spectroscopy and/or astrometry are needed to identify the best seismic solutions.« less
3. The MASSIVE Survey. XVII. A Triaxial Orbit-based Determination of the Black Hole Mass and Intrinsic Shape of Elliptical Galaxy NGC 2693

   https://doi.org/10.3847/1538-4357/ac58fd  

   Pilawa, Jacob D. ; Liepold, Christopher M. ; Delgado Andrade, Silvana C. ; Walsh, Jonelle L. ; Ma, Chung-Pei ; Quenneville, Matthew E. ; Greene, Jenny E. ; Blakeslee, John P. ( April 2022 , The Astrophysical Journal)

   We present a stellar dynamical mass measurement of a newly detected supermassive black hole (SMBH) at the center of the fast-rotating, massive elliptical galaxy NGC 2693 as part of the MASSIVE survey. We combine high signal-to-noise ratio integral field spectroscopy (IFS) from the Gemini Multi-Object Spectrograph with wide-field data from the Mitchell Spectrograph at McDonald Observatory to extract and model stellar kinematics of NGC 2693 from the central ∼150 pc out to ∼2.5 effective radii. Observations from Hubble Space Telescope WFC3 are used to determine the stellar light distribution. We perform fully triaxial Schwarzschild orbit modeling using the latest TriOS code and a Bayesian search in 6D galaxy model parameter space to determine NGC 2693's SMBH mass (M_BH), stellar mass-to-light ratio, dark matter content, and intrinsic shape. We find$M_{\mathrm{BH}}=\left(1.7\pm 0.4\right)\times {10}^9{M}_{\odot }$and a triaxial intrinsic shape with axis ratiosp=b/a= 0.902 ± 0.009 and$q=c/a={0.721}_{-0.010}^{+0.011}$, triaxiality parameterT= 0.39 ± 0.04. In comparison, the best-fit orbit model in the axisymmetric limit and (cylindrical) Jeans anisotropic model of NGC 2693 prefer$M_{\mathrm{BH}}=\left(2.4\pm 0.6\right)\times {10}^9{M}_{\odot }$and$M_{\mathrm{BH}}=\left(2.9\pm 0.3\right)\times {10}^9{M}_{\odot }$, respectively. Neither model can account for the non-axisymmetric stellar velocity features present inmore »the IFS data.

   « less
4. GJ 3929: High-precision Photometric and Doppler Characterization of an Exo-Venus and Its Hot, Mini-Neptune-mass Companion

   https://doi.org/10.3847/1538-4357/ac8480  

   Beard, Corey ; Robertson, Paul ; Kanodia, Shubham ; Lubin, Jack ; Cañas, Caleb I. ; Gupta, Arvind F. ; Holcomb, Rae ; Jones, Sinclaire ; Libby-Roberts, Jessica E. ; Lin, Andrea S. J. ; et al ( August 2022 , The Astrophysical Journal)

   We detail the follow-up and characterization of a transiting exo-Venus identified by TESS, GJ 3929b (TOI-2013b), and its nontransiting companion planet, GJ 3929c (TOI-2013c). GJ 3929b is an Earth-sized exoplanet in its star’s Venus zone (P_b= 2.616272 ± 0.000005 days; S_b=${17.3}_{-0.7}^{+0.8}$S_⊕) orbiting a nearby M dwarf. GJ 3929c is most likely a nontransiting sub-Neptune. Using the new, ultraprecise NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak National Observatory, we are able to modify the mass constraints of planet b reported in previous works and consequently improve the significance of the mass measurement to almost 4σconfidence (M_b= 1.75 ± 0.45M_⊕). We further adjust the orbital period of planet c from its alias at 14.30 ± 0.03 days to the likely true period of 15.04 ± 0.03 days, and we adjust its minimum mass to$m\sin i$= 5.71 ± 0.92M_⊕. Using the diffuser-assisted ARCTIC imager on the ARC 3.5 m telescope at Apache Point Observatory, in addition to publicly available TESS and LCOGT photometry, we are able to constrain the radius of planet b toR_p= 1.09 ± 0.04R_⊕. GJ 3929b is a top candidate for transmission spectroscopy in its size regime (TSM = 14more »± 4), and future atmospheric studies of GJ 3929b stand to shed light on the nature of small planets orbiting M dwarfs.

   « less
5. Turbulence in the Sub-Alfvénic Solar Wind

   https://doi.org/10.3847/2041-8213/ac51da  

   Zank, G. P. ; Zhao, L. -L. ; Adhikari, L. ; Telloni, D. ; Kasper, J. C. ; Stevens, M. ; Rahmati, A. ; Bale, S. D. ( February 2022 , The Astrophysical Journal Letters)

   The Parker Solar Probe (PSP) entered a region of sub-Alfvénic solar wind during encounter 8, and we present the first detailed analysis of low-frequency turbulence properties in this novel region. The magnetic field and flow velocity vectors were highly aligned during this interval. By constructing spectrograms of the normalized magnetic helicity, cross-helicity, and residual energy, we find that PSP observed primarily Alfvénic fluctuations, a consequence of the highly field-aligned flow that renders quasi-2D fluctuations unobservable to PSP. We extend Taylor’s hypothesis to sub- and super-Alfvénic flows. Spectra for the fluctuating forward and backward Elsässer variables (z^±, respectively) are presented, showing thatz⁺modes dominatez⁻by an order of magnitude or more, and thez⁺spectrum is a power law in frequency (parallel wavenumber)f^−3/2($k_{\parallel }^{-3/2}$) compared to the convexz⁻spectrum withf^−3/2($k_{\parallel }^{-3/2}$) at low frequencies, flattening around a transition frequency (at which the nonlinear and Alfvén timescales are balanced) tof^−1.25at higher frequencies. The observed spectra are well fitted using a spectral theory for nearly incompressible magnetohydrodynamics assuming a wavenumber anisotropy$k_{\perp }\sim k_{\parallel }^{3/4}$, that thez⁺fluctuations experience primarily nonlinear interactions, and that the minorityz⁻fluctuations experience both nonlinear and Alfvénic interactions withz⁺fluctuations. The density spectrum is a powermore »law that resembles neither thez^±spectra nor the compressible magnetic field spectrum, suggesting that these are advected entropic rather than magnetosonic modes and not due to the parametric decay instability. Spectra in the neighboring modestly super-Alfvénic intervals are similar.

   « less