Photometric Variability in the Faint Sky Variability Survey

The Faint Sky Variability Survey (FSVS) is aimed at finding photometric and/or astrometric variable objects between 16th and 24th mag on time-scales between tens of minutes and years with photometric precisions ranging from 3 millimag to 0.2 mag. An area of 23 deg$^2$, located at mid and high Galactic latitudes, was covered using the Wide Field Camera (WFC) on the 2.5-m Isaac Newton Telescope (INT) on La Palma. Here we present some preliminary results on the variability of sources in the FSVS.Comment: 4 pages, 3 figures, to appear in 14th European Workshop on White Dwarfs, ASP Conference Series, eds. D. Koester, S. Moehle

DE Canum Venaticorum: A Bright, Eclipsing Red Dwarf–White Dwarf Binary

Close white dwarf - red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf - red dwarf binary with a relatively short (~8.7 hours) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters which we discuss in the frame work of common-envelope evolution. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average low-resolution spectrum of DE CVn we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system

Investigating the function of single-pass leucine-rich repeat transmembrane proteins in cell signalling and early neural development

Single-pass leucine-rich (LRR) repeat transmembrane proteins contain a diverse number of repeating motifs of approximately 24 amino acid residues with a large number being conserved leucines. Flrt expression is observed in the developing embryo in important developmental regions such as the central nervous system and developing skeletal muscle. Knockout of Flrt3 during embryogenesis results in early embryonic lethality making in vivo analysis of endogenous Flrt3 function difficult. No cell based model exists for studying Flrt function. Flrt family members have previously been shown to interact with FgfR1 and 2, with the Flrt1 FgfR1 interaction resulting in an increase in FgfR1 signalling activity. Immunofluorescent microscopy reveals that Flrt3 from mouse (Mus musculus) co-localises with FgfR1 both intracellularly and at the plasma membrane, with the interaction resulting in a trend of increased FgfR1 signalling being observed, and phosphorylation of tyrosine residues within Flrt3. An attempt was made to identify domains of the protein important in the trend of increased FgfR1 signalling, but no domains could be identified as contributing to this outcome. To study endogenous Flrt3 function, the P19 embryonic carcinoma retinoic acid-induced neural differentiation model was used, and the results showed a rapid and robust induction of Flrt3 mRNA and protein expression. A region of the promoter between 4 kb and 6 kb upstream of the Flrt3 start site was found to be partially responsible for the induction of Flrt3. Interestingly, this response element was not within a region of promoter that showed conservation among higher-order mammals. An effect of increased Flrt3 expression during neural differentiation was observed, resulting in decreased MAPK pathway activation. Induction of Flrt3 is found to occur prior to that of Sox1, accepted to be one of the first genes up-regulated in early neurectoderm differentiation, yet was found to be not solely responsible for the induction of Sox1. The individual cell expression of Flrt3 and Sox1 was analysed by immunofluorescence, although it did not reveal details regarding induction of Sox1 in cells with increased Flrt3 expression. The potential for a common feature of single-pass LRR transmembrane proteins to function as modulators of receptor signalling during embryonic development was investigated, using Lrrtm3 and FgfR1 as an example. Lrrtm3 was investigated as a modulator of FgfR1 signalling due to overlapping region of expression with FgfR1 in the developing embryo. Lrrtm3 was found to co-localise and form an interaction with FgfR1, with this interaction resulting in an increase in FgfR1 signalling. The data obtained in this thesis provides further insight into not only the role of the Flrt protein family as FgfR1 modulators, but potentially identifies a role for similar, if not all single-pass LRR transmembrane proteins as regulators of receptor signalling during embryonic development. While the results of Chapter 3 and 5 were obtained using a protein over-expression system, the first model for studying endogenous Flrt3 was identified and characterised in Chapter 4, providing the opportunity to study Flrt3 function during development with protein expression levels closely resembling those that are found in the embryo.Thesis (M.Phil.) -- University of Adelaide, School of Biological Sciences, 201

Short timescale variability in the Faint Sky Variability Survey

We present the V band variability analysis of the point sources in the Faint Sky Variability Survey on time scales from 24 minutes to tens of days. We find that about one percent of the point sources down to V = 24 are variables. We discuss the variability detection probabilities for each field depending on field sampling, amplitude and timescale of the variability. The combination of colour and variability information allows us to explore the fraction of variable sources for different spectral types. We find that about 50 percent of the variables show variability timescales shorter than 6 hours. The total number of variables is dominated by main sequence sources. The distribution of variables with spectral type is fairly constant along the main sequence, with 1 per cent of the sources being variable, except at the blue end of the main sequence, between spectral types F0--F5, where the fraction of variable sources increases to about 2 percent. For bluer sources, above the main sequence, this percentage increases to about 3.5. We find that the combination of the sampling and the number of observations allows us to determine the variability timescales and amplitudes for a maximum of 40 percent of the variables found. About a third of the total number of short timescale variables found in the survey were not detected in either B or/and I. These show a similar variability timescale distribution to that found for the variables detected in all three bands.Comment: 14 pages, 12 figures and 4 tables. Accepted for publication in MNRA

Identification of 13 DB + dM and 2 DC + dM binaries from the Sloan Digital Sky Survey

We present the identification of 13 DB + dM binaries and 2 DC + dM binaries from the Sloan Digital Sky Survey (SDSS). Before the SDSS only 2 DB + dM binaries and 1 DC + dM binary were known. At least three, possibly 8, of the new DB + dM binaries seem to have white dwarf temperatures well above 30000 K which would place them in the so called DB-gap. Finding these DB white dwarfs in binaries may suggest that they have formed through a different evolutionary channel than the ones in which DA white dwarfs transform into DB white dwarfs due to convection in the upper layers.Comment: 4 pages, 2 figures, accepted for publication in A&A Letter

Recent improvements in the E-OBS gridded data set for daily mean wind speed over Europe in the period 1980–2021

In this work, we present the most recent updates in the E-OBS gridded data set for daily mean wind speed over Europe. The data set is provided as an ensemble of 20 equally likely realisations. The main improvements of this data set are the use of forward selection linear regression for the monthly background field, as well as a method to ensure the reliability of the ensemble dispersion. In addition, we make a preliminary study into possible causes of the observed terrestrial wind stilling effect, such as local changes in surface roughness length.</p

A ZZ Ceti white dwarf in SDSS J133941.11+484727.5

We present time-resolved spectroscopy and photometry of the cataclysmic variable (CV) SDSSJ133941.11+484727.5 (SDSS1339) which has been discovered in the Sloan Digital Sky Survey Data Release 4. The orbital period determined from radial velocity studies is 82.524(24)min, close to the observed period minimum. The optical spectrum of SDSS1339 is dominated to 90% by emission from the white dwarf. The spectrum can be successfully reproduced by a three-component model (white dwarf, disc, secondary) with Twd=12500K for a fixed log g=8.0, d=170pc, and a spectral type of the secondary later than M8. The mass transfer rate corresponding to the optical luminosity of the accretion disc is very low,~1.7x10^-13Msun/yr. Optical photometry reveals a coherent variability at 641s with an amplitude of 0.025mag, which we interpret as non-radial pulsations of the white dwarf. In addition, a long-period photometric variation with a period of either 320min or 344min and an amplitude of 0.025mag is detected, which bears no apparent relation with the orbital period of the system. Similar long-period photometric signals have been found in the CVs SDSSJ123813.73-033933.0, SDSSJ204817.85-061044.8, GW Lib and FS Aur, but so far no working model for this behaviour is available.Comment: MNRAS, in press, 8 pages, 10 figures, some figures downgraded to meet the file size constraint of arxiv.or

DE Canum Venaticorum : a bright, eclipsing red dwarf–white dwarf binary

Context. Close white dwarf–red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf–red dwarf binary with a relatively short (∼8.7 h) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study. Aims. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters that we discuss in the framework of common-envelope evolution. Methods. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average lowresolution spectrum of DE CVn, we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system. Results. The derived ephemeris is HJDmin = 2 452 784.5533(1) + 0.3641394(2) × E. The red dwarf in DE CVn has a spectral type of M3V and the white dwarf has an effective temperature of 8 000 K. The inclination of the system is 86+3◦ −2 and the mass and radius of the red dwarf are 0.41 ± 0.06 M and 0.37+0.06 −0.007 R, respectively, and the mass and radius of the white dwarf are 0.51+0.06 −0.02 M and 0.0136+0.0008 −0.0002 R, respectively. Conclusions. We found that the white dwarf has a hydrogen-rich atmosphere (DA-type). Given that DE CVn has experienced a common-envelope phase, we can reconstruct its evolution and we find that the progenitor of the white dwarf was a relatively lowmass star (M ≤ 1.6 M). The current age of this system is 3.3−7.3 × 109 years, while it will take longer than the Hubble time for DE CVn to evolve into a semi-detached system

Downward shortwave radiation trends in Europe since the 20th century: what we know from direct measurements and sunshine duration records?

Póster presentado en: AGU Fall Meeting celebrado en San Francisco del 15 al 19 de diciembre de 2014.This work was supported by the Ministry of Economy and Competitiveness of the Government of Spain through the projects NUCLIERSOL (CGL2010-18546) and HIDROCAES (CGL2011-27574-CO2-02). The first author was supported by the “Secretaria per a Universitats i Recerca del Departament d’Economia i Coneixement, de la Generalitat de Catalunya i del programa Cofund de les Accions Marie Curie del 7è Programa marc d’R+D de la Unión Europea” (2011 BP-B 00078) and the postdoctoral fellowship JCI-2012-12508. ASR received a grant from the FPU program (FPU AP2010-0917) of the Spanish Ministry of Education

Downward shortwave radiation trends in Europe since the 20th century: what we know from direct measurements and sunshine duration records?

The first part of this work presents results based on the longest series measuring downward shortwave radiation (DSR) available at the Global Energy Balance Archive (GEBA) over Europe, some of them available since the 1920s. Particular emphasis is placed upon the quality control and homogenization of the dataset, which has been checked for temporal homogeneity by means of different relative homogeneity tests. The mean annual DSR series show an increase from the 1930s to the early 1950s (i.e. early brightening period), followed by a reduction until mid-1980s (i.e., dimming period), and ending with an increase up to the present (i.e., brightening period). Overall, the trend from the 1930s to the present is negative and significant on annual basis. Unfortunately, there exists a substantial gap in direct measurements of DSR as few stations in Europe provide records before the 1960s. To overcome the lack of direct measurements, the analysis can be supported with other proxy variables more widely measured, such as sunshine duration (SD) records. Thus, in this work we also present the reconstructed DSR variations since late 19th century in Europe based on the SD series over Europe with around one century of records, some of them starting in the 1880s. The reconstructed DSR variations have been estimated by using the relationship found between the SD sunshine duration series and a satellite-derived DSR dataset (0.03 x 0.03 of spatial resolution), provided by the EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF), during the common 1983-2005 subperiod. The reconstructed records have been validated by using the GEBA series described in the first part of this work. The temporal evolution of the mean DSR annual series since the 1950s is characterized by the well-known dimming and brightening periods. Moreover, an early brightening period is also detected during the first half of the 20th century, although regional differences are observed with areas over Europe where the DSR show no increase in this subperiod. Interestingly, the reconstructed DSR also highlight an absolute minimum in 1912, which should be the signal of the Katmai volcanic eruption (i.e., largest volcanic eruption in the 20th century) as the consequence of the direct effect of the volcanic sulphur aerosols released in the volcanic eruption. The results highlight the suitability of SD records to detect changes in DSR under all-sky and clear-sky conditions (e.g., due to aerosol changes)