178 research outputs found
Career situation of female astronomers in Germany
We survey the job situation of women in astronomy in Germany and of German
women abroad and review indicators for their career development. Our sample
includes women astronomers from all academic levels from doctoral students to
professors, as well as female astronomers who have left the field. We find that
networking and human support are among the most important factors for success.
Experience shows that students should carefully choose their supervisor and
collect practical knowledge abroad. We reflect the private situation of female
German astronomers and find that prejudices are abundant, and are perceived as
discriminating.We identify reasons why women are more likely than men to quit
astronomy after they obtain their PhD degree. We give recommendations to young
students on what to pay attention to in order to be on the successful path in
astronomy.Comment: published in Astronomical Note
Careers in astronomy in Germany and the UK
We discuss the outcomes of surveys addressing the career situation of
astronomers in Germany and the UK, finding social and cultural differences
between communities as well as gender bias in both.Comment: Astronomy and Geophysics. 13 page pdf with colour image
Effects of dating errors on nonparametric trend analyses of speleothem time series
A fundamental problem in paleoclimatology is to take fully into account the various error sources when examining proxy records with quantitative methods of statistical time series analysis. Records from dated climate archives such as speleothems add extra uncertainty from the age determination to the other sources that consist in measurement and proxy errors. This paper examines three stalagmite time series of oxygen isotopic composition (&delta;<sup>18</sup>O) from two caves in western Germany, the series AH-1 from the Atta Cave and the series Bu1 and Bu4 from the Bunker Cave. These records carry regional information about past changes in winter precipitation and temperature. U/Th and radiocarbon dating reveals that they cover the later part of the Holocene, the past 8.6 thousand years (ka). We analyse centennial- to millennial-scale climate trends by means of nonparametric Gasser–Müller kernel regression. Error bands around fitted trend curves are determined by combining (1) block bootstrap resampling to preserve noise properties (shape, autocorrelation) of the &delta;<sup>18</sup>O residuals and (2) timescale simulations (models StalAge and iscam). The timescale error influences on centennial- to millennial-scale trend estimation are not excessively large. We find a "mid-Holocene climate double-swing", from warm to cold to warm winter conditions (6.5 ka to 6.0 ka to 5.1 ka), with warm–cold amplitudes of around 0.5&permil; &delta;<sup>18</sup>O; this finding is documented by all three records with high confidence. We also quantify the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the current warmth. Our analyses cannot unequivocally support the conclusion that current regional winter climate is warmer than that during the MWP
Vegetation dynamics amplifies precessional forcing
The astronomical theory of climate variations predicts that the climatic precession which changes the seasonal distance between Earth and Sun does not affect the annual mean irradiation at any given latitude. However, previous modeling studies suggest that during interglacials, the interaction between atmosphere, vegetation and ocean can transform the seasonal forcing by precession into an annual mean global signal. Here, we show that this result can be generalized. A distinct precessional signal emerges in a climate system model over many precessional cycles. While neither the atmosphere-ocean nor the atmosphere-vegetation model are able to produce a large amplitude of global temperature in the precessional band, only the mutual amplification of biogeophysical feedback and sea ice- albedo feedback allows a strong amplification of the precessional signa
The Rewards of Patience: An 822 Day Time Delay in the Gravitational Lens SDSS J1004+4112
We present 107 new epochs of optical monitoring data for the four brightest
images of the gravitational lens SDSS J1004+4112 observed between October 2006
and June 2007. Combining this data with the previously obtained light curves,
we determine the time delays between images A, B and C. We confirm our previous
measurement finding that A leads B by dt_BA=40.6+-1.8 days, and find that image
C leads image A by dt_CA=821.6+-2.1 days. The lower limit on the remaining
delay is that image D lags image A by dt_AD>1250 days. Based on the
microlensing of images A and B we estimate that the accretion disk size at a
rest wavelength of 2300 angstrom is 10^{14.8+-0.3} cm for a disk inclination of
cos{i}=1/2, which is consistent with the microlensing disk size-black hole mass
correlation function given our estimate of the black hole mass from the MgII
line width of logM_BH/M_sun=8.44+-0.14. The long delays allow us to fill in the
seasonal gaps and assemble a continuous, densely sampled light curve spanning
5.7 years whose variability implies a structure function with a logarithmic
slope of gamma = 0.35+-0.02. As C is the leading image, sharp features in the C
light curve can be intensively studied 2.3 years later in the A/B pair,
potentially allowing detailed reverberation mapping studies of a quasar at
minimal cost.Comment: Submitted to ApJ, 12 pages, 3 figure
Non-parametric strong lens inversion of SDSS J1004+4112
In this article we study the well-known strong lensing system SDSS
J1004+4112. Not only does it host a large-separation lensed quasar with
measured time-delay information, but several other lensed galaxies have been
identified as well. A previously developed strong lens inversion procedure that
is designed to handle a wide variety of constraints, is applied to this lensing
system and compared to results reported in other works. Without the inclusion
of a tentative central image of one of the galaxies as a constraint, we find
that the model recovered by the other constraints indeed predicts an image at
that location. An inversion which includes the central image provides tighter
constraints on the shape of the central part of the mass map. The resulting
model also predicts a central image of a second galaxy where indeed an object
is visible in the available ACS images. We find masses of 2.5x10^13 M_O and
6.1x10^13 M_O within a radius of 60 kpc and 110 kpc respectively, confirming
the results from other authors. The resulting mass map is compatible with an
elliptical generalization of a projected NFW profile, with r_s = 58_{-13}^{+21}
arcsec and c_vir = 3.91 +/- 0.74. The orientation of the elliptical NFW profile
follows closely the orientation of the central cluster galaxy and the overall
distribution of cluster members.Comment: 11 pages, accepted for publication in MNRA
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The Longest Delay: A 14.5 yr Campaign to Determine the Third Time Delay in the Lensing Cluster SDSS J1004+4112
We present new light curves for the four bright images of the five image cluster-lensed quasar gravitational lens system SDSS J1004+4112. The light curves span 14.5 yr and allow the measurement of the time delay between the trailing bright quasar image D and the leading image C. When we fit all four light curves simultaneously and combine the models using the Bayesian information criterion, we find a time delay of Δt DC = 2458.47 ± 1.02 days (6.73 yr), the longest ever measured for a gravitational lens. For the other two independent time delays we obtain Δt BC = 782.20 ± 0.43 days (2.14 yr) and Δt AC = 825.23 ± 0.46 days (2.26 yr), in agreement with previous results. The information criterion is needed to weight the results for light curve models with different polynomial orders for the intrinsic variability and the effects of differential microlensing. The results using the Akaike information criterion are slightly different, but, in practice, the absolute delay errors are all dominated by the ∼4% cosmic variance in the delays rather than the statistical or systematic measurement uncertainties. Despite the lens being a cluster, the quasar images show slow differential variability due to microlensing at the level of a few tenths of a magnitude
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Erratum: "The Longest Delay: A 14.5 yr Campaign to Determine the Third Time Delay in the Lensing Cluster SDSS J1004+4112" (2022, ApJ, 937, 34)
[no abstract available
A Novel Frequency Analysis Method for Assessing Kir2.1 and Nav1.5 Currents
Voltage clamping is an important tool for measuring individual currents from an electrically active cell. However, it is difficult to isolate individual currents without pharmacological or voltage inhibition. Herein, we present a technique that involves inserting a noise function into a standard voltage step protocol, which allows one to characterize the unique frequency response of an ion channel at different step potentials. Specifically, we compute the fast Fourier transform for a family of current traces at different step potentials for the inward rectifying potassium channel, Kir2.1, and the channel encoding the cardiac fast sodium current, Nav1.5. Each individual frequency magnitude, as a function of voltage step, is correlated to the peak current produced by each channel. The correlation coefficient vs. frequency relationship reveals that these two channels are associated with some unique frequencies with high absolute correlation. The individual IV relationship can then be recreated using only the unique frequencies with magnitudes of high absolute correlation. Thus, this study demonstrates that ion channels may exhibit unique frequency responses
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