98,120 research outputs found
Joshua Davis: Author of Spare Parts
No full textCitation: K-State First (2016). Joshua Davis: Author of Spare Parts [Flier]. Manhattan, Kansas: K-State First.Flyer advertising Joshua Davis's author talk at Kansas State University
Steven Johnson Author Talk Poster
No full textK-State Book NetworkA poster advertising an author talk by Steven Johnson at Kansas State University on September 3, 2014. Steven Johnson's book "The Ghost Map" was the 2014-2015 common book
The narrowest M-dwarf line profiles and the rotation-activity connection at very slow rotation
No full textContext.The rotation-activity connection explains stellar activity in terms
of rotation and convective overturn time. It is well established
in stars of spectral types F–K as well as in M-type stars of
young clusters, in which rotation is still very rapid even among
M-dwarfs. The rotation-activity connection is not established in
field M-dwarfs, because they rotate very slowly, and detecting
rotation periods or rotational line broadening is a challenge. In
field M-dwarfs, saturation sets in below vrot =
5 km s-1, hence they are expected to populate the
non-saturated part of the rotation-activity connection.
Aims.This work for the first time shows intrinsically resolved spectral
lines of slowly rotating M-dwarfs and makes a first comparison to
estimates of convective velocities. By measuring rotation
velocities in a sample of mostly inactive M-dwarfs, the
unsaturated part of the rotation-activity connection is followed
into the regime of very low activity.
Methods.Spectra of ten M-dwarfs are taken at a resolving power of at the CES in the near infrared region where molecular
FeH has strong absorption bands. The intrinsically very narrow
lines are compared to model calculations of convective flows, and
rotational broadening is measured.
Results.In one star, an upper limit of = 1 km s-1 was
found, significant rotation was detected in the other nine
objects. All inactive stars show rotation below or equal to
2 km s-1. In the two active stars AD Leo and YZ CMi,
rotation velocities are found to be 40–50% below the results
from earlier studies.
Conclusions. The rotation activity connection holds in field early-M stars,
too. Activity and rotation velocities of the sample stars are
well in agreement with the relation found in earlier and younger
stars. The intrinsic absorption profiles of molecular FeH lines
are consistent with calculations from atomic Fe lines.
Investigation of FeH line profiles is a very promising tool to
measure convection patterns at the surfaces of M-stars
A laser-lock concept to reach cm s
No full textState-of-the-art Doppler experiments require wavelength calibration with precision at the
cm s-1 level. A
low-finesse Fabry-Pérot interferometer (FPI) can provide a wavelength comb with a very
large bandwidth as required for astronomical experiments, but unavoidable spectral drifts
are difficult to control. Instead of actively controlling the FPI cavity, we propose to
passively stabilize the interferometer and track the time-dependent cavity length drift
externally using the 87Rb D2 atomic line. A dual-finesse cavity
allows drift tracking during observation. In the low-finesse spectral range, the cavity
provides a comb transmission spectrum tailored to the astronomical spectrograph. The drift
of the cavity length is monitored in the high-finesse range relative to an external
standard: a single narrow transmission peak is locked to an external cavity diode laser
and compared to an atomic frequency from a Doppler-free transition. Following standard
locking schemes, tracking at sub-mm s-1 precision can be achieved. This is several orders of
magnitude better than currently planned high-precision Doppler experiments, and it allows
freedom for relaxed designs including the use of a single-finesse interferometer under
certain conditions. All components for the proposed setup are readily available, rendering
this approach particularly interesting for upcoming Doppler experiments. We also show that
the large number of interference modes used in an astronomical FPI allows us to
unambiguously identify the interference mode of each FPI transmission peak defining its
absolute wavelength solution. The accuracy reached in each resonance with the laser
concept is then defined by the cavity length that is determined from the one locked peak
and by the group velocity dispersion. The latter can vary by several
100 m s-1 over
the relevant frequency range and severely limits the accuracy of individual peak
locations, although their interference modes are known. A potential way to determine the
absolute peak positions is to externally measure the frequency of each individual peak
with a laser frequency comb (LFC). Thus, the concept of laser-locked FPIs may be useful
for applying the absolute accuracy of an LFC to astronomical spectrographs without the
need for an LFC at the observatory
Understanding the Set Consensus Partial Order Using the Borowsky-Gafni Simulation (Extended Abstract)
No full text) Soma Chaudhuri and Paul Reiners Iowa State University, Ames, IA 50011, USA Abstract. We present a complete characterization of the Set Consensus Partial Order, a refinement of the Consensus Hierarchy of Herlihy. We define the (n; k)-set consensus problem as the k-set consensus problem for n processors. We then answer the question of whether an (n; k)- set consensus object (an object which solves the (n; k)-set consensus problem) can be implemented using a combination of (m; `)-set consensus objects and snapshot objects, for all possible values of n; k; m; `, creating a partial order of set consensus objects. The model we consider is the asynchronous shared memory model. To prove our results, we use the Borowsky-Gafni Simulation technique, a powerful tool which has been used to prove several impossibility results about shared memory algorithms. Lynch and Rajsbaum gave a formal description of the basic technique, along with a proof of its correctness. We extend their results to inclu..
On the kinematic age of brown dwarfs: radial velocities and space motions of 43 nearby L dwarfs
No full textWe present radial velocity measurements of a sample of L0–L8 dwarfs
observed with VLT/UVES and Keck/HIRES. We combine these measurements
with distance and proper motion from the literature to determine
space motions for 43 of our targets. We identify nine candidate
members of young moving groups, which have ages of 50–600 Myr according to their
space motion. From the total velocity dispersion of the 43 L dwarfs,
we calculate a kinematic age of ~5 Gyr for our sample. This age
is significantly higher than the ~3 Gyr age known for late M
dwarfs in the solar neighbourhood. We find that the distributions of
the U and V velocity components of our sample are clearly
non-Gaussian, placing the age estimate inferred from the full space motion
vector into question. The W-component exhibits a distribution more
consistent with a normal distribution, and from W alone we derive
an age of ~3 Gyr, which is the same age found for late-M dwarf
samples. Our brightness-limited sample is probably contaminated by a
number of outliers that predominantly bias the U and V velocity
components. The origin of the outliers remain unclear, but we
suggest that these brown dwarfs may have gained their high velocities
by means of ejection from multiple systems during their formation
The IAG solar flux atlas: Accurate wavelengths and absolute convective blueshift in standard solar spectra
No full textWe present a new solar flux atlas with the aim of understanding wavelength precision and accuracy in solar benchmark data. The atlas covers the wavelength range 405−2300 nm and was observed at the Institut für Astrophysik, Göttingen (IAG), with a Fourier transform spectrograph (FTS). In contrast to other FTS atlases, the entire visible wavelength range was observed simultaneously using only one spectrograph setting. We compare the wavelength solution of the new atlas to the Kitt Peak solar flux atlases and to the HARPS frequency-comb calibrated solar atlas. Comparison reveals systematics in the two Kitt Peak FTS atlases resulting from their wavelength scale construction, and shows consistency between the IAG and the HARPS atlas. We conclude that the IAG atlas is precise and accurate on the order of ± 10 m s-1 in the wavelength range 405−1065 nm, while the Kitt Peak atlases show deviations as large as several ten to 100 m s-1. We determine absolute convective blueshift across the spectrum from the IAG atlas and report slight differences relative to results from the Kitt Peak atlas that we attribute to the differences between wavelength scales. We conclude that benchmark solar data with accurate wavelength solution are crucial to better understand the effect of convection on stellar radial velocity measurements, which is one of the main limitations of Doppler spectroscopy at m s -1 precision
On detectability of Zeeman broadening in optical spectra of F- and G-dwarfs
No full textWe investigate the detectability of Zeeman broadening in optical Stokes I spectra of slowly rotating sun-like stars. To this end, we apply the LTE spectral line inversion package SPINOR to very-high quality CES data and explore how fit quality depends on the average magnetic field, Bf. One-component (OC) and two-component (TC) models are adopted. In OC models, the entire surface is assumed to be magnetic. Under this assumption, we determine formal 3 sigma upper limits on the average magnetic field of 200G for the Sun, and 150 G for 61 Vir (G6V). Evidence for an average magnetic field of similar to 500 G is found for 59 Vir (G0V), and of similar to 1000G for HD68456 (F6V). A distinction between magnetic and non-magnetic regions is made in TC models, while assuming a homogeneous distribution of both components. In our TC inversions of 59 Vir, we investigate three cases: both components have equal temperatures; warm magnetic regions; cool magnetic regions. Our TC model with equal temperatures does not yield significant improvement over OC inversions for 59 Vir. The resulting Bf values are consistent for both. Fit quality is significantly improved, however, by using two components of different temperatures. The inversions for 59 Vir that assume different temperatures for the two components yield results consistent with 0-450 G at the formal 3 sigma confidence level. We thus find a model dependence of our analysis and demonstrate that the influence of an additional temperature component can dominate over the Zeeman broadening signature, at least in optical data. Previous comparable analyses that neglected effects due to multiple temperature components may be prone to the same ambiguities
Der Einfluss verschiedener Facetten mathematischer Kenntnisse und Kompetenzen auf den Prüfungserfolg im ersten Semester
No full textGasteiger H, Salle A, Reiners S. Der Einfluss verschiedener Facetten mathematischer Kenntnisse und Kompetenzen auf den Prüfungserfolg im ersten Semester. In: Binder K, Frank A, Krauss S, eds. Beiträge zum Mathematikunterricht 2019. Regensburg, Deutschland: GDM; 2019: 1059–1062
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