Stokes' Phenomenon arising from the confluence of two simple poles

We study certain confluences of equations with two Fuchsian singularities which produce an irregular singularity of Poincaré rank one. We demonstrate a method to understand how to pass from solutions with power-like behavior which are analytic in neighbourhoods to solutions with exponential behavior which are analytic in sectors and have divergent asymptotic behavior. We explicitly calculate the Stokes' matrices of the confluent system in terms of the monodromy data, specifically the connection matrices, of the original system around the merging singularities. The confluence of Gauss' hypergeometric equation gives an excellent opportunity to show our approach with a concrete example. We explicitly show how the Stokes' data arise in the confluences of the isomonodromic deformation problems for the Painlevé equations PVI to PV and PV to PIII(D6)

A study of T Tauri stars with multiple spectral types and their surface temperatures

This thesis describes the results of two spectral studies of T Tauri stars. T Tauri stars are young, low mass, stars which have yet to evolve to the point where Hydrogen fusion occurs in their cores. They are normally found in groups associated with gas clouds in locations called star forming regions. Much work has been done to explain the bizarre spectral features of T Tauri stars, and this has led to the development of a standard model for their structures. Classical T Tauri stars are thought to be surrounded by large discs of accreting material, which slowly adds to the mass of the star. This accretion process results in large U.V. and I.R. fluxes for the stars when compared to their main sequence counterparts. Weak-line T Tauri stars do not display any accretion features and are thought to be more evolved than Classical T Tauri stars. Observations show that both types of T Tauri star have active chromospheres and large cool spots, which are both thought to be a result of strong magnetic fields. This thesis is motivated by two studies, one spectroscopic, one photometric, both of which suggest that some T Tauri stars display photospheric features from regions of different temperatures, or multiple spectral types (MST).The first spectral study discussed is of near-I.R. data taken with UKIRT. The spectra are of high resolution data from the region around 1.63 fim, and are of T Tauri, giant and dwarf stars of known spectral type. It is shown that a ratio of selected OH to Fe lines gives a good trend with the optically measured Te//> derived from spectral types, for both dwarfs and giants. Whilst some of the T Tauri stars fit this trend, it is found that 4 stars clearly lie above it. This is taken as an indication of cooler regions in the spectra than had previously been detected, an MST effect.The second spectral study discussed is of optical data taken with the FLAIR system on the UKST. The spectra span the entire optical region observable with this instrument, and are intended to show variation in temperature sensitive features between the blue and red optical regions. Spectra are presented from 2 consecutive nights of observations and previously discovered MST stars are found to show deeper G bands than would be predicted from the TiO bands in the red spectra. It is found that the G band of one object has varied both on a night to night basis and since the previous observations from the mid-1980’s. It is also shown that no variation has occurred in the red spectraAll of the information on MST stars is then compared in order to determine the best physical model for the effect. It is shown that none of the regions in the standard model of Classical T Tauri stars can produce the MTS features. The first model considered that could display MTS features is of binary systems of stars with differing spectral type, but equivalent flux in the optical. It is found that these systems would be too rare to explain all the MTS results. The large cool spots seen on T Tauri stars are also considered as the cause of the MST effect. It is shown that the size of spots required is much greater than the size of observed cool regions. The current theories of solar active regions are discussed, revealing that the dominant photospheric regions are in fact the small, bright faculae. Whilst the spectra of solar faculae are still not fully understood it is found that a faculae+photosphere+cool spot model of T Tauri spectra can produce all the observed MST effects.Finally, the systematic errors in the H-R diagram introduced by the MST effect are considered. By comparison with research on dwarf stars it is found that the MST effects do not significantly alter the stellar Tef f and luminosity. The largest errors are introduced if only a small wavelength region is considered when determining the spectral type of the star. Studies that derive a Te/ / from an apparent spectral type and ignore the MST effect can both over and underestimate Te/ / ; leading to a possible factor of 2 error in the stellar mass. As T Tauri spectral parameters are also used to derive the overall features of star forming regions, this can lead to the miscalculation of the mass function and ages of these regions

Line and Continuum Variability in Active Galaxies

We compared optical spectroscopic and photometric data for 18 AGN galaxies over 2 to 3 epochs, with time intervals of typically 5 to 10 years. We used the Multi-Object Double Spectrograph (MODS) at the Large Binocular Telescope (LBT) and compared the spectra to data taken from the SDSS database and the literature. We find variations in the forbidden oxygen lines as well as in the hydrogen recombination lines of these sources. For 4 of the sources we find that, within the calibration uncertainties, the variations in continuum and line spectra of the sources are very small. We argue that it is mainly the difference in black hole mass between the samples that is responsible for the different degree of continuum variability. In addition we find that for an otherwise constant accretion rate the total line variability (dominated by the narrow line contributions) reverberates the continuum variability with a dependency $\Delta L_{line} \propto (\Delta L_{cont.})^{\frac{3}{2}}$. Since this dependency is prominently expressed in the narrow line emission it implies that the luminosity dominating part of the narrow line region must be very compact with a size of the order of at least 10 light years. A comparison to literature data shows that these findings describe the variability characteristics of a total of 61 broad and narrow line sources.Comment: 30 pages including the appendix, 18 figures including the appendix. Accepted 2015 September 3. Received 2015 August 24; in original form 2015 July 3 in Monthly Notices of the Royal Astronomical Societ

SUBARU and e-Merlin observations of NGC3718. Diaries of an SMBH recoil?

NGC3718 is a LINER $L1.9$ galaxy, lying at a distance of about $\sim 17.4$ Mpc away from earth and its similarities with NGC5128 often award it the name "northern Centaurus A". We use high angular resolution ($\sim100$ mas) e-Merlin radio and SUBARU NIR ($\sim170$ mas) data, to take a detailed view of the processes taking place in its central region. In order to preserve some objectivity in our interpretation, we combine our results with literature values and findings from previous studies. Our NIR maps suggest, on one hand, that towards the stellar bulge there are no large scale absorption phenomena caused by the apparent dust lane and, on the other, that there is a significant (local) contribution from hot ($\sim1000$ K) dust to the nuclear NIR emission. The position where this takes place appears to be closer to the offset compact radio emission from our e-Merlin $6$ cm map, lying offset by $\sim4.25$ pc from the center of the underlying stellar bulge. The shape of the radio map suggests the presence of one (or possibly two, forming an X-shape) bipolar structure(s) $\sim1$ ($\sim0.6$) arcsec across, which combined with the balance between the gas and the stellar velocity dispersions and the presence of hard X-ray emission, point towards effects expected by AGN feedback. We also argue that NGC3718 has a "core" in its surface brightness profile, despite the fact that it is a gas-rich galaxy and we discuss its mixed photometric and spectroscopic characteristics. The latter combined with the observed spatial and radio offsets, the relative redshift between the broad and the narrow $H{\mathrm{\alpha}}$ line, the limited star formation activity and AGN feedback, strongly imply the existence of an SMBH recoil. Finally, we discuss a possible interpretation, that could naturally incorporate all these findings into one physically consistent picture.Comment: 18 pages, 18 figures, 3 tables, accepted for publications in A&

Sequential star formation in IRAS 06084-0611 (GGD 12-15): From intermediate-mass to high-mass stars

Context. The formation and early evolution of high- and intermediate-mass stars towards the main sequence involves the interplay of stars in a clustered and highly complex environment. To obtain a full census of this interaction, the Formation and Early evolution of Massive Stars (FEMS) collaboration studies a well-selected sample of 10 high-mass star-forming regions. Aims. In this study we examine the stellar content of the high-mass star-forming region centered on IRAS 06084-0611 in the Monoceros R2 cloud. Methods. Using the near-infrared H- and K-band spectra from the VLT/SINFONI instrument on the ESO Very Large Telescope (VLT)and photometric near-infrared NTT/SOFI, 2MASS and Spitzer/IRAC data, we were able to determine the spectral types for the most luminous stars in the cluster. Results. Two very young and reddened massive stars have been detected by SINFONI: a massive Young Stellar Object (YSO) con- sistent with an early-B spectral type and a Herbig Be star. Furthermore, stars of spectral type G and K are detected while still in the Pre-Main Sequence (PMS) phase. We derive additional properties such as temperatures, extinctions, radii and masses. We present a Hertzsprung-Russell diagram and find most objects having intermediate masses between \sim1.5-2.5 M\odot. For these stars we derive a median cluster age of \sim4 Myr. Conclusions. Using Spitzer/IRAC data we confirm earlier studies that the younger class 0/I objects are centrally located while the class II objects are spread out over a larger area, with rough scale size radii of \sim0.5 pc and \sim1.25 pc respectively. Moreover, the presence of a massive YSO, an ultracompact H ii region and highly reddened objects in the center of the cluster suggest a much younger age of < 1 Myr. A possible scenario for this observation would be sequential star formation along the line of sight; from a cluster of intermediate-mass to high-mass stars.Comment: 14 pages, 10 figures, 2 tables. Astronomy and Astrophysic

Peer-review in a world with rational scientists: Toward selection of the average

One of the virtues of peer review is that it provides a self-regulating selection mechanism for scientific work, papers and projects. Peer review as a selection mechanism is hard to evaluate in terms of its efficiency. Serious efforts to understand its strengths and weaknesses have not yet lead to clear answers. In theory peer review works if the involved parties (editors and referees) conform to a set of requirements, such as love for high quality science, objectiveness, and absence of biases, nepotism, friend and clique networks, selfishness, etc. If these requirements are violated, what is the effect on the selection of high quality work? We study this question with a simple agent based model. In particular we are interested in the effects of rational referees, who might not have any incentive to see high quality work other than their own published or promoted. We find that a small fraction of incorrect (selfish or rational) referees can drastically reduce the quality of the published (accepted) scientific standard. We quantify the fraction for which peer review will no longer select better than pure chance. Decline of quality of accepted scientific work is shown as a function of the fraction of rational and unqualified referees. We show how a simple quality-increasing policy of e.g. a journal can lead to a loss in overall scientific quality, and how mutual support-networks of authors and referees deteriorate the system.Comment: 5 pages 4 figure