Thomas M Amby

Eclipsing binaries are one of our primary sources for accurate stellar masses and radii. Typically it is possible to determine the component masses and radii better than 1 - 2 %. With reliable effective temperatures and detailed abundances also available, stringent tests of stellar evolution models become possible.
The aim of the project is to analyse the systems AL Leo and DS And. AL Leo is interesting since the cooler secondary component is bigger than the hotter primary component. Hence this system might reveal more information about convective core overshoot. Regarding DS And this open cluster member has an extremely high rotational velocity v(rot)*sin i = 106 km/s. I aim at providing a better solution for the systems than what have been published before, and I should at least reach an accuracy of 1 - 2 % of the absolute dimensions.
The systems have been analysed photometrically using the Wilson-Devinney code as well as spectroscopically by the means of broadening functions.

The recently discovered subdwarf B (sdB) pulsator KIC11558725 features a rich g-mode frequency spectrum, with a few low-amplitude p-modes at short periods, and is a promising target for a seismic study aiming to constrain the internal structure of this star, and of sdB stars in general.
We have obtained ground-based spectroscopic Balmer-line radial-velocity measurements of KIC11558725, spanning the 2010 and 2011 observing seasons. From these data we have discovered that KIC11558725 is a binary with period P=10.05 d, and that the radial-velocity amplitude of the sdB star is 58 km/s. Consequently the companion of the sdB star has a minimum mass of 0.63 M\odot, and is therefore most likely an unseen white dwarf.
We analyse the near-continuous 2010-2011 Kepler light curve to reveal orbital Doppler-beaming light variations at the 238 ppm level, which is consistent with the observed spectroscopic orbital radial-velocity amplitude of the subdwarf. We use the strongest 70 pulsation frequencies in the Kepler light curve of the subdwarf as clocks to derive a third consistent measurement of the orbital radial-velocity amplitude, from the orbital light-travel delay.
We use our high signal-to-noise average spectra to study the atmospheric parameters of the sdB star, deriving Teff = 27 910K and log g = 5.41 dex, and find that carbon, nitrogen and oxygen are underabundant relative to the solar mixture.
Furthermore, we extract more than 160 significant frequencies from the Kepler light curve. We investigate the pulsation frequencies for expected period spacings and rotational splittings. We find period-spacing sequences of spherical-harmonic degrees \ell=1 and \ell=2, and we associate a large fraction of the g-modes in KIC11558725 with these sequences. From frequency splittings we conclude that the subdwarf is rotating subsynchronously with respect to the orbit.

The electrification of wind-blown dust grains was studied in a series of laboratory experiments to examine how grain electrification depends on grain size, grain mineralogy, atmospheric composition, atmospheric pressure, and the method of dust dispersal. This work is intended to contribute to a deeper physical understanding of particle electrification on both Mars and Earth. Findings indicate that the amount of electrification per suspended particle generally is independent of dust entrainment process and atmospheric composition. As expected, the electrification process is grain size-dependent, with smaller grains predominantly electrifying negatively. Although there appears to be a weak dependence upon dust mineralogy, this work supports the expectation that dust suspended in the Martian atmosphere will be significantly electrified.

We present the recent discovery of a new subdwarf B variable (sdBV), with an exceptionally low surface gravity. Our spectroscopy of J20136+0928 places it at Teff = 32100 +/- 500, log(g) = 5.15 +/- 0.10, and log(He/H) = -2.8 +/- 0.1. With a magnitude of B = 12.0, it is the second brightest V361 Hya star ever found. Photometry from three different observatories reveals a temporal spectrum with eleven clearly detected periods in the range 376 to 566 s, and at least five more close to our detection limit. These periods are unusually long for the V361 Hya class of short-period sdBV pulsators, but not unreasonable for p- and g-modes close to the radial fundamental, given its low surface gravity. Of the ~50 short period sdB pulsators known to date, only a single one has been found to have comparable spectroscopic parameters to J20136+0928. This is the enigmatic high-amplitude pulsator V338 Ser, and we conclude that J20136+0928 is the second example of this rare subclass of sdB pulsators located well above the canonical extreme horizontal branch in the HR diagram.

For the survey phase of the Kepler Mission, three groups submitted proposals containing candidate hot subdwarf and white dwarf stars. Of the stars included in these proposals, 142 were accepted into the list of KASC survey stars. Of these, six were observed during the 9.7d commissioning run, and 57 were observed during the first four (out of 10) survey months. All 63 stars are listed in Table 1.

We present results from the final six months of a survey to search for pulsations in white dwarfs and hot subdwarf stars with the Kepler spacecraft. Spectroscopic observations are used to separate the objects into accurate classes, and we explore the physical parameters of the subdwarf B (sdB) stars and white dwarfs in the sample. From the Kepler photometry and our spectroscopic data, we find that the sample contains 5 new pulsators of the V1093 Her type, one AM CVn type cataclysmic variable, and a number of other binary systems. This completes the survey for compact pulsators with Kepler. No V361 Hya type of short-period pulsating sdB stars were found in this half, leaving us with a total of one single multiperiodic V361 Hya and 13 V1093 Her pulsators for the full survey. Except for the sdB pulsators, no other clearly pulsating hot subdwarfs or white dwarfs were found, although a few low amplitude candidates still remain. The most interesting targets discovered in this survey will be observed throughout the remainder of the Kepler Mission, providing the most longterm photometric datasets ever made on such compact, evolved stars. Asteroseismic investigations of these datasets will be invaluable in revealing the interior structure of these stars, and will boost our understanding of their evolutionary history.

We present results from the first two quarters of a survey to search for pulsations in compact stellar objects with the Kepler spacecraft. The survey sample and the various methods applied in its compilation are described, and spectroscopic observations are presented to separate the objects into accurate classes. From the Kepler photometry we clearly identify nine compact pulsators, and a number of interesting binary stars. Of the pulsators, one shows the strong, rapid pulsations typical for a V361 Hya type sdB variable (sdBV), seven show long-period pulsations characteristic of V1093 Her type sdBVs, and one shows low-amplitude pulsations with both short and long periods. We derive effective temperatures and surface gravities for all the subdwarf B stars in the sample and demonstrate that below the boundary region where hybrid sdB pulsators are found, all our targets are pulsating. For the stars hotter than this boundary temperature a low fraction of strong pulsators (<10 per cent) is confirmed. Interestingly, the short-period pulsator also shows a low-amplitude mode in the long-period region, and several of the V1093 Her pulsators show low amplitude modes in the short-period region, indicating that hybrid behaviour may be common in these stars, also outside the boundary temperature region where hybrid pulsators have hitherto been found.

The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions like massive white dwarfs (M > 1.0 Msun), neutron stars or stellar mass black holes. The existence of such systems is predicted by binary evolution theory and recent discoveries indicate that they exist in our Galaxy. First results are presented for seven close binary sdBs with short orbital periods ranging from 0.21 d to 1.5 d. The atmospheric parameters of all objects are compatible with core helium-burning stars. The companions are most likely white dwarfs. In one case the companion could be shown to be a white dwarf by the absence of light-curve variations. However, in most cases late type main sequence stars cannot be firmly excluded. Comparing our small sample with the known population of close sdB binaries we show that our target selection method aiming at massive companions is efficient. The minimum companion masses of all binaries in our sample are high compared to the reference sample of known sdB binarie

The three eclipsing binary systems AB And, BD And and CG Cyg were observed using the FIES instrument on the NOT telescope during 5 nights of August, 2008. The aim was to derive radial velocities for the systems using photometric data at two di®erent phases, and from that obtain estimates of the components' individual masses. Our results gave only three data points for two of the objects, AB And and BD And, and the estimated values were obtained for these.

In this exercise we create a stellar model with the solar surface values of mass, radius and luminosity, while the surface pressure, density and eective temperature are derived from these values. This yields a model that accurately resembles that of table 11.2 in Christensen-Dalsgaard (2006) in the outer and middle parts of the model star, but begins to deviate as we approach closer to the core, eventually diverging completely. We modify the surface conditions by setting the surface luminosity to 0:85L and the surface radius to 0:9467R, to get a model the approaches m = 0 and L = 0 at r = 0. Finally we choose several values for the surface luminosity and search for models of varying radii which display zero or negative mass in the core, thereby revealing the location of the Hayashi track.

Øvelsen og rapporten er delt op i to dele. Formålet med første del af øvelsen er beskrive dannelsen af femtosekund laserpulser samt at karakterisere de dannede laserpulser. Sammenhængen mellem den spektrale bredde og pulslængden undersøges og de forventede værdier beregnes. Formålet med den anden del af øvelsen er at bruge femtosekund laserpulserne til at lave struktur i en silicon overade, således at der dannes en kopi af en gur.

At lave en ny pointing model for et teleskop er tidskrævende arbejde, men det er samtidig alt arbejdet værd når teleskopet bare virker. Arbejdet med at lave en ny pointing model falder i flere etaper og det kan være svært at nå det hele på en enkelt nat med godt vejr. Den første process i at bestemme en ny pointing model er at genoplinierer teleskopets akser. Dette gøres for at sikre stabil og sikker tracking efterfølgende således at det bliver muligt at foretage længere observatorer uden at miste objektet af syne eller få star trails, såfremt man benytter CCD’er til observatorerne. Man skal på regne ca. 1 nat til at opliniere teleskopets akser. Den anden del er at skabe en ny pointing model. Dette kræver mest tid at mappe alle stjernerne men efterhånden som man får mappet flere og flere stjerner vil man kunne se en mærkbar fremgang i pointingen af teleskopet. Sidst i denne rapport følger et afsnit om hvorledes man med en relativt beskeden investering kan opgradere ORO til at kunne bruge i endnu videre udstrækning i undervisningen. Det foreslåes bl.a. at købe en ny CCD som vil udvide FOV fra 8 × 6 bueminutter til 22 × 16, 6 bueminutter.

In this paper we are presenting the results and work conducted on 27th of September
2010. A series of three different experiments were conducted in order to characterise
a diode of the type BYV26E PH from Phillips Semiconductors. The diode is a silicon
based semiconductor with an unknown doping, used to make the diode response faster.
We will present the results of our investigation of this diode and also try to determine
the doping used to dope the silicon. The three experiments conducted were a C-V
characteristic which determined the capacitance of the diode to be 22.51 ± 0.14pF.
Which is consistent with what is shown in the data sheet of the diode provided by
Phillips Semiconductors. The second experiment conducted were an I-V characteristic,
in order to determine the current needed to switch the diode from the off state to the
on state. From this characteristic we can also estimate the thermal voltage, VT =
2.5 mV, of the diode, this turn out to be consistent with theory with an accuracy
of 3.4 %. We find that the point when the diode switches state from off to on is
determined to be roughly equal to VT The last type of experiment is a deep level
transient spectroscopy, from this we find the energy gap in the diode to be −(Ec−Et) =
−0.1768±0.0026 and −(Ec −Et) = −0.4864±0.0162 respectively, which is consistent
with those induced by doping the silicon with Tellurium, e.g. −(Ec − Et) = −0.1987
and −(Ec − Et) = −0.4112 respectively. Here by we see that our results are not
conclusive and with a somewhat more cumbersome investigation one might be able to
determine the contaminant more decisively.

During this paper we will be presenting the results of the experiment conducted on September 6th, 2010. The purpose of the exercise was to investigate contact electrification in an environment different from our atmosphere. The experiment was conducted at the \ML at Aarhus University, where we worked on state of the art equipment. The experiment consisted of two different parts, one where we contact electrification of grained Icelandic Basalt using the Laser Anemometer and Martian Dust Collector ~(hence LAMDA) instrument, for instrument specifications Merrison et al., 2006, p. 1066 - 1067 or section 4.1 in this paper. A commercial Laser Doppler Anemometer (henceforth LDA) was used acquire the suspension time, tau, for a detailed description of this instrument see Merrison et al., 2006, p. 1067. For the analysis we have used Matlab. The analysis have been divided into two sections. First getting the suspension time from the LDA measurements and afterwards using the LAMDA ~data to estimate the contact electrification both negative and positive Q+/-. The results we are presenting here are quite remarkable in the sense that typical experiments of this kind are conducted in atmospheric conditions resembling those of other planets or moons, e.g. Mars or Titan. To achieve atmospheric conditions like those of Mars experiments have to go down to a pressure of ~ 10 mbar, in our experiment we are using a pressure of only ~ 100 mbar. That manifests itself directly by a greater suspension time, than what would normally be expected. We find the suspension time is constrained to be between 15.5 min and 18 min, and we find that the electrification is Q+ = -15345.424 and Q- = 14599.118

Through out resent year the use of computer models and simulations have been used in a far larger extend, in galactic astronomy, than what we have seen before. Therefore I will investigate the probabilities of such simulations. The main focus of this paper is the writing of a efficient computer code, and the validation of it. The purpose of the code is to study the stellar orbits in galaxies. We also want to investigate different computational methods, and then validate our code by comparing to with figures from Binney and Tremaine (2008). We have chosen to write the code in Python since
Python is a script language like Matlab most of the syntax is identical to that of Matlab, the major difference is that Python is the free alternative. I find that the code produces reliable results and that we can learn something about galaxies from these types of models.
We find that we can recreate earlier results and we notice that there is a lot of unexplored aspects of this field of astronomy. But we get some remarkable results. Improvements left for the future is to do a frequency analysis of the oscillations, since that will give an even better determination of what is a good and stable orbit and which are not.

Since the middle of the 1940’s scientists have used Monte Carlo (MC) simulations to obtain information about physical processes. This has proved a accurate and and reliable method to obtain this information. Through out resent years researchers has begone to use the slightly newer Markov Chain Monte Carlo (MCMC) simulation. This differs from the ordinary MC by using the Markov Chain. MCMC originates from Bayesian statistics. This method has given researchers a completely new tool to learn something about physical systems. One of the fields where MCMC is a good new tool, is astrophysics. Today MCMC is widely used in simulating power spectra for asteroseismic data. Hereby providing the scientists with important new information of stellar interiors. From our results we see that MCMC delivers a robust and reliable result with good error estimation. We also learn that MCMC is a power full tool which can be applied to a large verity of problems.

In the 1980’s a new field of astronomy saw the light for the first time. When astronomers suggested that was possible to get information about the stellar interior from studying the stellar fluctuations on ultra short time scale, and applying the tools of seismology. To study sound waves propagating in the stellar interior. This led to a completely new way of studying stars. The first star
which was investigated was the Sun.The Sun proved to be a brilliant test case for this new field of astronomy. Since it is possible to resolve the surface of the sun even with ground based telescopes. The new field of research was called Helioseismology. It turned out that it was possible for the astronomers to get information about the interior of the stars. Something that Sir Arthur Eddington claimed to be impossible with his statement:

“At first sight it would seam that the deep interior if the
Sun and stars is less accessible to scientific investigation
than any other region of our universe. Our telescopes
may probe farther and farther into the depths of space:
but how can we ever obtain certain knowledge of that
which is hidden behind substantial barriers? What appliance can pierce the outer layers of a start and test the conditions within?”

So Eddington was indeed wrong. The next big step came
when astronomers started to apply seismologic techniques to other stars than the sun, and thereby moved the field from helioseismology into what is now known as astroseismology. Astroseismology have certain constrains and limitations, but it is a very easy way of determine certain fundamental parameters for the star which we are investigating. Through this paper a numerical code will be developed, it will be developed for MatLab.

Gennem tiden har mange forfattere tænkt over hvordan man kommer til Månen.
Dette har givet anledning til nogle sjove/sære idéer. Jeg vil i dette kollokvium kigge
nærmere på nogle af dem. Vi drager altså på en rejse i tiden og ser på udviklingen
fra Jules Verne, over Hergé til den egentlige måne færd med Apollo
rumprogrammet. Jeg vil beskrive hvordan man kommer til Månen, hvad det vil sige
at være vægtløs og ikke mindst hvordan man navigere i rummet. Foredraget vil
være rigt illustreret, med både billeder og lyde fra historien.