25 research outputs found
Using a model for telluric absorption in full-spectrum fits
The typical approach for removing telluric absorption lines from a science
spectrum is to divide it by the spectrum of a standard star of spectral type A
or B observed close in time and airmass. We present a new method, where we use
a model for the transmission of the Earth's atmosphere in a full-spectrum fit,
which determines the parameters for the stellar and Earth's atmosphere
simultaneously. This eliminates the need of a standard star completely.Comment: 4 pages, 3 figures, International Workshop on Stellar Spectral
Libraries 201
The central dynamics of M3, M13, and M92: Stringent limits on the masses of intermediate-mass black holes
We used the PMAS integral field spectrograph to obtain large sets of radial
velocities in the central regions of three northern Galactic globular clusters:
M3, M13, and M92. By applying the novel technique of crowded field 3D
spectroscopy, we measured radial velocities for about 80 stars within the
central ~ 10 arcsec of each cluster. These are by far the largest spectroscopic
datasets obtained in the innermost parts of these clusters up to now. To obtain
kinematical data across the whole extent of the clusters, we complement our
data with measurements available in the literature. We combine our velocity
measurements with surface brightness profiles to analyse the internal dynamics
of each cluster using spherical Jeans models, and investigate whether our data
provide evidence for an intermediate-mass black hole in any of the clusters.
The surface brightness profiles reveal that all three clusters are consistent
with a core profile, although shallow cusps cannot be excluded. We find that
spherical Jeans models with a constant mass-to-light ratio provide a good
overall representation of the kinematical data. A massive black hole is
required in none of the three clusters to explain the observed kinematics. Our
1sigma (3sigma) upper limits are 5300 M_sun (12000 M_sun) for M3, 8600 M_sun
(13000 M_sun) for M13, and 980 M_sun (2700 M_sun) for M92. A puzzling
circumstance is the existence of several potential high velocity stars in M3
and M13, as their presence can account for the majority of the discrepancies
that we find in our mass limits compared to M92.Comment: accepted for publication in A&A, 20 pages, 15 figures, tables D1 to
D6 only available at CD
Discovery of an old nova remnant in the Galactic globular cluster M 22
A nova is a cataclysmic event on the surface of a white dwarf in a binary
system that increases the overall brightness by several orders of magnitude.
Although binary systems with a white dwarf are expected to be overabundant in
globular clusters (GCs) compared to the Galaxy, only two novae from Galactic
globular clusters have been observed. We present the discovery of an emission
nebula in the Galactic globular cluster M 22 (NGC 6656) in observations made
with the integral-field spectrograph MUSE. We extract the spectrum of the
nebula and use the radial velocity determined from the emission lines to
confirm that the nebula is part of NGC 6656. Emission-line ratios are used to
determine the electron temperature and density. It is estimated to have a mass
of 1 to solar masses. This mass and the emission-line
ratios indicate that the nebula is a nova remnant. Its position coincides with
the reported location of a 'guest star', an ancient Chinese term for
transients, observed in May 48 BCE. With this discovery, this nova may be one
of the oldest confirmed extrasolar events recorded in human history.Comment: 7 pages, 3 figures; accepted for publication in Astronomy &
Astrophysic
Kinematic differences between multiple populations in Galactic globular clusters
The formation process of multiple populations in globular clusters is still
up for debate. Kinematic differences between the populations are particularly
interesting in this respect, because they allow us to distinguish between
single-epoch formation scenarios and multi-epoch formation scenarios. We
analyze the kinematics of 25 globular clusters and aim to find kinematic
differences between multiple populations to constrain their formation process.
We split red-giant branch (RGB) stars in each cluster into three populations
(P1, P2, P3) for the type-II clusters and two populations (P1 and P2) otherwise
using Hubble photometry. We derive the rotation and dispersion profiles for
each cluster and its populations by using all stars with radial velocity
measurements obtained from MUSE spectroscopy. Based on these profiles, we
calculate the rotation strength in terms of ordered-over-random motion
evaluated at the half-light radius of the
cluster. We detect rotation in all but four clusters. For NGC~104, NGC~1851,
NGC~2808, NGC~5286, NGC~5904, NGC~6093, NGC~6388, NGC~6541, NGC~7078 and
NGC~7089 we also detect rotation for P1 and/or P2 stars. For NGC~2808, NGC~6093
and NGC~7078 we find differences in between
P1 and P2 that are larger than . Whereas we find that P2 rotates
faster than P1 for NGC~6093 and NGC~7078, the opposite is true for NGC~2808.
However, even for these three clusters, the differences are still of low
significance. We find that the strength of rotation of a cluster generally
scales with its median relaxation time. For P1 and P2, the corresponding
relation is very weak at best. We observe no correlation between the difference
in rotation strength between P1 and P2 and cluster relaxation time. The MUSE
stellar radial velocities that this analysis is based on are made publicly
available
A stellar census in globular clusters with MUSE: Binaries in NGC 3201
We utilize multi-epoch MUSE spectroscopy to study binaries in the core of NGC
3201. Our sample consists of 3553 stars with 54883 spectra in total comprising
3200 main-sequence stars up to 4 magnitudes below the turn-off. Each star in
our sample has between 3 and 63 (with a median of 14) reliable radial velocity
(RV) measurements within five years of observations. We introduce a statistical
method to determine the probability of a star showing RV variations based on
the whole inhomogeneous RV sample. Using HST photometry and an advanced
dynamical MOCCA simulation of this specific GC we overcome observational biases
that previous spectroscopic studies had to deal with. This allows us to infer a
binary frequency in the MUSE FoV and enables us to deduce the underlying true
binary frequency of (6.75+-0.72) % in NGC 3201. The comparison of the MUSE
observations with the MOCCA simulation suggests a significant fraction of
primordial binaries. We can also confirm a radial increase of the binary
fraction towards the GC centre due to mass segregation. We discovered that in
our sample at least (57.5+-7.9) % of blue straggler stars (BSS) are in a binary
system. For the first time in a study of GCs, we were able to fit Keplerian
orbits to a significant sample of 95 binaries. We present the binary system
properties of eleven BSS and show evidence that two BSS formation scenarios,
the mass transfer in binary (or triple) star systems and the coalescence due to
binary-binary interactions, are present in our data. We also describe the
binary and spectroscopic properties of four sub-subgiant (or red straggler)
stars. Furthermore, we discovered two new black hole (BH) candidates with
minimum masses (Msini) of (7.68+-0.50) M_sun, (4.4+-2.8) M_sun, and refine the
minimum mass estimate on the already published BH to (4.53+-0.21) M_sun. These
BHs are consistent with an extensive BH subsystem hosted by NGC 3201
Hazy with a chance of star spots: constraining the atmosphere of the young planet, K2-33b
Although all-sky surveys have led to the discovery of dozens of young
planets, little is known about their atmospheres. Here, we present
multi-wavelength transit data for the super Neptune-sized exoplanet, K2-33b --
the youngest (~10 Myr) transiting exoplanet to-date. We combined photometric
observations of K2-33 covering a total of 33 transits spanning >2 years, taken
from K2, MEarth, Hubble, and Spitzer. The transit photometry spanned from the
optical to the near-infrared (0.6-4.5m), enabling us to construct a
transmission spectrum of the planet. We find that the optical transit depths
are nearly a factor of two deeper than those from the near-infrared. This
difference holds across multiple datasets taken over years, ruling out issues
of data analysis and unconstrained systematics. Surface inhomogeneities on the
young star can reproduce some of the difference, but required spot coverage
fractions (>60%) are ruled out by the observed stellar spectrum(<20%). We find
a better fit to the transmission spectrum using photochemical hazes, which were
predicted to be strong in young, moderate-temperature, and large-radius planets
like K2-33b. A tholin haze with CO as the dominant gaseous carbon carrier in
the atmosphere can reasonably reproduce the data with small or no stellar
surface inhomogeneities, consistent with the stellar spectrum. The HST data
quality is insufficient for the detection of any molecular features. More
observations would be required to fully characterize the hazes and spot
properties and confirm the presence of CO suggested by current data.Comment: Accepted to AJ. 26 pages, 14 figures, 6 table
A detached stellar-mass black hole candidate in the globular cluster NGC 3201
Large scale structure and cosmolog
3D-Spectroscopy of Dense Stellar Populations
Softcover, 17x24, 194 S.: 30,00 €Softcover, 17x24Globular clusters are gravitationally bound collections of hundreds of thousands of stars that are almost as old as the Universe itself. Although they have been studied for hundreds of years, their formation and evolution is not yet fully understood. We want to find answers to some of the major questions by investing a large amount of observing time with MUSE, the upcoming 2nd generation instrument for ESO‘s Very Large Telescope. In this thesis I discuss the current state of research on globular clusters as well as the possibilities of this new instrument. Numerical methods for the analysis of MUSE data are presented, including a comprehensive library of synthetic spectra that has been created just for this purpose. The application of these methods to both synthetic and real data is discussed with particular emphasis on a „dry run“ that has been conducted for MUSE. Finally, a potential program for the observation of globular clusters is presented