13 research outputs found
Se med SONG fra ORO
I 2006 lød startskuddet til et verdensomspændende projekt ledet af forskere fra Aarhus Universitet og Københavns Universitet. Projektet fik navnet SONG, som står for “Stellar Observations Network Group”. På Ole Rømer-Observatoriet har “Stellar Astrophysics Centre” i samarbejde med Science Museerne opstillet et kontrolrum, hvorfra SONG-teleskopet kan styres, og observationer kan udføres. Astronom Mads Fredslund Andersen fra Institut for Fysik og Astronomi, AU, fortæller her om SONG og forbindelsen til Ole Rømer-Observatoriet
FX UMa: A New Heartbeat Binary System with Linear and Non-linear Tidal Oscillations and delta Sct Pulsations
We present a detailed analysis of an eclipsing double-lined binary FX UMa
based on TESS photometry and newly acquired spectroscopic observations. The
radial velocities and atmospheric parameters for each component star are
obtained from the SONG high-resolution spectra. Combined with the
radial-velocity measurements, our light-curve modeling yields absolute masses
and radii of the two components. The Fourier amplitude spectrum of the residual
light curve reveals a total of 103 frequencies with signal-to-noise ratio (S/N)
> 4, including 12 independent frequencies, 17 multiples of the orbital
frequency (Nforb), and 74 combination frequencies. Ten Nforb peaks with S/N >
10 have very high amplitudes and are likely due to tidally excited oscillations
(TEOs). The remaining Nforb peaks (4 < S/N < 10) may be originated from the
imperfect removal, or they are actually real TEOs. Four anharmonic frequencies
can pair up and sum to give exact harmonics of the orbital frequency,
suggesting the existence of non-linear tidal processes in the eccentric binary
system FX UMa. Eight independent frequencies in the range of 20 to 32
day are typical low-order pressure modes of delta Scuti pulsators.Comment: 15+4 pages, 8 figures, Submitted to AJ
Precise radial velocities of giant stars XV. Mysterious nearly periodic radial velocity variations in the eccentric binary Cygni
Using the Hamilton Echelle Spectrograph at Lick Observatory, we have obtained
precise radial velocities (RVs) of a sample of 373 G- and K-giant stars over
more than 12 years, leading to the discovery of several single and multiple
planetary systems. The RVs of the long-period (~53 years) spectroscopic binary
Cyg (HIP 102488) are found to exhibit additional regular variations
with a much shorter period (~291 days). We intend to improve the orbital
solution of the Cyg system and attempt to identify the cause of the
nearly periodic shorter period variations, which might be due to an additional
substellar companion. We used precise RV measurements of the K-giant star
Cyg from Lick Observatory, in combination with a large set of RVs
collected more recently with the SONG telescope, as well as archival data sets.
Our Keplerian model to the RVs characterizes the orbit of the spectroscopic
binary to higher precision than achieved previously, resulting in a semi-major
axis of , an eccentricity of , and a minimum
mass of the secondary of . Additional short-period RV
variations closely resemble the signal of a Jupiter-mass planet orbiting the
evolved primary component with a period of , but the period and
amplitude of the putative orbit change strongly over time. Furthermore, in our
stability analysis of the system, no stable orbits could be found in a large
region around the best fit. Both of these findings deem a planetary cause of
the RV variations unlikely. Most of the investigated alternative scenarios,
such as an hierarchical triple or stellar spots, also fail to explain the
observed variability convincingly. Due to its very eccentric binary orbit, it
seems possible, however, that Cyg could be an extreme example of a
heartbeat system.Comment: 17 pages, 13 figures, accepted to A&
Aldebaran b's temperate past uncovered in planet search data
The nearby red giant Aldebaran is known to host a gas giant planetary
companion from decades of ground-based spectroscopic radial velocity
measurements. Using Gaussian Process-based Continuous Auto-Regressive Moving
Average (CARMA) models, we show that these historic data also contain evidence
of acoustic oscillations in the star itself, and verify this result with
further dedicated ground-based spectroscopy and space-based photometry with the
Kepler Space Telescope. From the frequency of these oscillations we determine
the mass of Aldebaran to be , and note that this
implies its planet will have been subject to insolation comparable to the Earth
for some of the star's main sequence lifetime. Our approach to sparse,
irregularly sampled time series astronomical observations has the potential to
unlock asteroseismic measurements for thousands of stars in archival data, and
push to lower-mass planets around red giant stars.Comment: 24 pages, 7 figures (including appendices); submitted to ApJL; paper
text, figures, data, and code at https://github.com/farr/Aldebara
Parameters of the eclipsing binary α Draconis observed by TESS and SONG
We present an analysis of the eclipsing single-lined spectroscopic binary system α Dra based on photometry from the Transiting Exoplanet Survey Satellite (TESS) mission and newly acquired spectroscopic measurements. Recently discovered to have eclipses in the TESS data, at a magnitude of V = 3.7, α Dra is now one of the brightest detached eclipsing binary (EB) systems known. We obtain the parameters of this system by simultaneously fitting the TESS light curve in conjunction with radial velocities (RVs) acquired from the SONG spectrograph. We determine the fractional radii (R/a) for the primary and secondary components of the system to be 0.0479 ± 0.0003 and 0.0226 ± 0.0005, respectively. We constrain the temperature, mass, and luminosity (log(L/L⊙)) of the primary to be 9975±125 K, 3.7±0.1 M⊙, and 2.49±0.02, respectively, using isochrone fitting. Although the secondary is too faint to appear in the spectra, the obtained mass function and observed inclination yields a secondary minimum mass of M2=2.5±0.1 M⊙, which suggests that it is an A2V type star. We were unable to obtain RVs of the secondary, and are only able to see a weak highly rotationally broadened absorption line, indicating that the secondary is rapidly rotating (vsin i ∼ 200 km s−1). We also perform an abundance analysis of the primary star for 21 chemical elements. We find a complex abundance pattern, with a few elements having mild underabundances while the majority have solar abundances. We make available the PYTHON code used in this paper to facilitate future modelling of EBs
Asteroseismic masses of four evolved planet-hosting stars using SONG and TESS: resolving the retired A-star mass controversy
The study of planet occurrence as a function of stellar mass is important for
a better understanding of planet formation. Estimating stellar mass, especially
in the red giant regime, is difficult. In particular, stellar masses of a
sample of evolved planet-hosting stars based on spectroscopy and grid-based
modelling have been put to question over the past decade with claims they were
overestimated. Although efforts have been made in the past to reconcile this
dispute using asteroseismology, results were inconclusive. In an attempt to
resolve this controversy, we study four more evolved planet-hosting stars in
this paper using asteroseismology, and we revisit previous results to make an
informed study of the whole ensemble in a self-consistent way. For the four new
stars, we measure their masses by locating their characteristic oscillation
frequency, , from their radial velocity time
series observed by SONG. For two stars, we are also able to measure the large
frequency separation, , helped by extended SONG single-site
and dual-site observations and new TESS observations. We establish the
robustness of the -only-based results by
determining the stellar mass from , and from both
and . We then compare the
seismic masses of the full ensemble of 16 stars with the spectroscopic masses
from three different literature sources. We find an offset between the seismic
and spectroscopic mass scales that is mass-dependent, suggesting that the
previously claimed overestimation of spectroscopic masses only affects stars
more massive than about 1.6 M.Comment: 13 pages, 12 figures, Accepted for publication in the Main Journal of
MNRA
An immunogenic first-in-human immune modulatory vaccine with PD-L1 and PD-L2 peptides is feasible and shows early signs of efficacy in follicular lymphoma
Cells in the tumor microenvironment of Follicular lymphoma (FL) express checkpoint molecules such as programmed death ligands 1 and 2 (PD-L1 and PD-L2) and are suppressing anti-tumor immune activity. Stimulation of peripheral blood mononuclear cells (PBMC) with PD-L1 (IO103) or PD-L2 (IO120) peptides can activate specific T cells inducing anti-regulatory functions including cytotoxicity against PD-L1/PD-L2-expressing cells. In this study, we vaccinated eight FL patients with PD-L1 and PD-L2 peptides following treatment with standard chemotherapy. Patients experienced grade 1–2 injection site reaction (5/8) and mild flu-like symptoms (6/8). One patient experienced neutropenia and thrombocytopenia during pseudo-progression. Enzyme-linked immunospot detected vaccine-specific immune responses in PBMC from all patients, predominately toward PD-L1. The circulating immune composition was stable during treatment; however, we observed a reduction regulatory T cells, however, not significant. One patient achieved a complete remission during vaccination and two patients had pseudo-progression followed by long-term disease regression. Further examination of these early signs of clinical efficacy of the dual-epitope vaccine in a larger study is warranted