53 research outputs found
Asteroseismic estimate of helium abundance of a solar analog binary system
16 Cyg A and B are among the brightest stars observed by Kepler. What makes
these stars more interesting is that they are solar analogs. 16 Cyg A and B
exhibit solar-like oscillations. In this work we use oscillation frequencies
obtained using 2.5 years of Kepler data to determine the current helium
abundance of these stars. For this we use the fact that the helium ionization
zone leaves a signature on the oscillation frequencies and that this signature
can be calibrated to determine the helium abundance of that layer. By
calibrating the signature of the helium ionization zone against models of known
helium abundance, the helium abundance in the envelope of 16 Cyg A is found to
lie in the range 0.231 to 0.251 and that of 16 Cyg B lies in the range 0.218 to
0.266.Comment: Accepted for publication in Ap
Solving the mode identification problem in asteroseismology of F stars observed with Kepler
Asteroseismology of F-type stars has been hindered by an ambiguity in
identification of their oscillation modes. The regular mode pattern that makes
this task trivial in cooler stars is masked by increased linewidths. The
absolute mode frequencies, encapsulated in the asteroseismic variable epsilon,
can help solve this impasse because the values of epsilon implied by the two
possible mode identifications are distinct. We find that the correct epsilon
can be deduced from the effective temperature and the linewidths and we apply
these methods to a sample of solar-like oscillators observed with Kepler.Comment: 7 pages, 4 figures, 1 table, accepted for publication in The
Astrophysical Journal Letter
Kepler-21b: A 1.6REarth Planet Transiting the Bright Oscillating F Subgiant Star HD 179070
We present Kepler observations of the bright (V=8.3), oscillating star HD
179070. The observations show transit-like events which reveal that the star is
orbited every 2.8 days by a small, 1.6 R_Earth object. Seismic studies of HD
179070 using short cadence Kepler observations show that HD 179070 has a
frequencypower spectrum consistent with solar-like oscillations that are
acoustic p-modes. Asteroseismic analysis provides robust values for the mass
and radius of HD 179070, 1.34{\pm}0.06 M{\circ} and 1.86{\pm}0.04 R{\circ}
respectively, as well as yielding an age of 2.84{\pm}0.34 Gyr for this F5
subgiant. Together with ground-based follow-up observations, analysis of the
Kepler light curves and image data, and blend scenario models, we
conservatively show at the >99.7% confidence level (3{\sigma}) that the transit
event is caused by a 1.64{\pm}0.04 R_Earth exoplanet in a 2.785755{\pm}0.000032
day orbit. The exoplanet is only 0.04 AU away from the star and our
spectroscopic observations provide an upper limit to its mass of ~10 M_Earth
(2-{\sigma}). HD 179070 is the brightest exoplanet host star yet discovered by
Kepler.Comment: Accepted to Ap
First Perihelion of EUI on the Solar Orbiter mission
Context. The Extreme Ultraviolet Imager (EUI), onboard Solar Orbiter consists
of three telescopes: the two High Resolution Imagers in EUV (HRIEUV) and in
Lyman-{\alpha} (HRILya), and the Full Sun Imager (FSI). Solar Orbiter/EUI
started its Nominal Mission Phase on 2021 November 27. Aims. EUI images from
the largest scales in the extended corona off limb, down to the smallest
features at the base of the corona and chromosphere. EUI is therefore a key
instrument for the connection science that is at the heart of the Solar Orbiter
mission science goals. Methods. The highest resolution on the Sun is achieved
when Solar Orbiter passes through the perihelion part of its orbit. On 2022
March 26, Solar Orbiter reached for the first time a distance to the Sun close
to 0.3 au. No other coronal EUV imager has been this close to the Sun. Results.
We review the EUI data sets obtained during the period 2022 March-April, when
Solar Orbiter quickly moved from alignment with the Earth (2022 March 6), to
perihelion (2022 March 26), to quadrature with the Earth (2022 March 29). We
highlight the first observational results in these unique data sets and we
report on the in-flight instrument performance. Conclusions. EUI has obtained
the highest resolution images ever of the solar corona in the quiet Sun and
polar coronal holes. Several active regions were imaged at unprecedented
cadences and sequence durations. We identify in this paper a broad range of
features that require deeper studies. Both FSI and HRIEUV operate at design
specifications but HRILya suffered from performance issues near perihelion. We
conclude emphasising the EUI open data policy and encouraging further detailed
analysis of the events highlighted in this paper
Seismic analysis of four solar-like stars observed during more than eight months by Kepler
Having started science operations in May 2009, the Kepler photometer has been
able to provide exquisite data of solar-like stars. Five out of the 42 stars
observed continuously during the survey phase show evidence of oscillations,
even though they are rather faint (magnitudes from 10.5 to 12). In this paper,
we present an overview of the results of the seismic analysis of 4 of these
stars observed during more than eight months.Comment: 5 pages, 1 figure. To appear in the ASP proceedings of "The 61st
Fujihara seminar: Progress in solar/stellar physics with helio- and
asteroseismology", 13th-17th March 2011, Hakone, Japa
Age dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi
Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies1. Although these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to date precisely the age at which any one merger occurred. Recent results have revealed a population of stars that were accreted via the collision of a dwarf galaxy, called Gaia–Enceladus1, leading to substantial pollution of the chemical and dynamical properties of the Milky Way. Here we identify the very bright, naked-eye star ν Indi as an indicator of the age of the early in situ population of the Galaxy. We combine asteroseismic, spectroscopic, astrometric and kinematic observations to show that this metal-poor, alpha-element-rich star was an indigenous member of the halo, and we measure its age to be 11.0±0.7 (stat) ±0.8 (sys) billion years. The star bears hallmarks consistent with having been kinematically heated by the Gaia–Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 billion years ago, at 68% and 95% confidence, respectively. Computations based on hierarchical cosmological models slightly reduce the above limits
Slow Solar Wind Connection Science during Solar Orbiter’s First Close Perihelion Passage
The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilize the extensive suite of remote-sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote-sensing and in situ measurements of slow wind originating at open–closed magnetic field boundaries. The SOOP ran just prior to Solar Orbiter’s first close perihelion passage during two remote-sensing windows (RSW1 and RSW2) between 2022 March 3–6 and 2022 March 17–22, while Solar Orbiter was at respective heliocentric distances of 0.55–0.51 and 0.38–0.34 au from the Sun. Coordinated observation campaigns were also conducted by Hinode and IRIS. The magnetic connectivity tool was used, along with low-latency in situ data and full-disk remote-sensing observations, to guide the target pointing of Solar Orbiter. Solar Orbiter targeted an active region complex during RSW1, the boundary of a coronal hole, and the periphery of a decayed active region during RSW2. Postobservation analysis using the magnetic connectivity tool, along with in situ measurements from MAG and SWA/PAS, showed that slow solar wind originating from two out of three of the target regions arrived at the spacecraft with velocities between ∼210 and 600 km s−1. The Slow Wind SOOP, despite presenting many challenges, was very successful, providing a blueprint for planning future observation campaigns that rely on the magnetic connectivity of Solar Orbiter
Astrodynamical Space Test of Relativity Using Optical Devices I (ASTROD I)—A class-M fundamental physics mission proposal for Cosmic Vision 2015–2025
Flag Hare-And Exercise: on the Extraction of Sectoral Mode Splittings from Full-Disc Sun-As Data
International audienc
Asteroseismic estimate of helium abundance of 16 Cyg A, B
The helium ionization zone in a star leaves a characteristic signature on its oscillation frequencies, which can be used to estimate the helium content in the envelope of the star. We use the oscillation frequencies of 16 Cyg A and B, obtained using 2.5 years of Kepler data, to estimate the envelope helium abundance of these stars. We find the envelope helium abundance to lie in the range 0.231–0.251 for 16 Cyg A and 0.218–0.266 for 16 Cyg B
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