517 research outputs found
Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.)
The accurate reconstruction of sea surface temperature (SST) history in climate-sensitive regions (e.g. tropical and polar oceans) became a challenging task in palaeoceanographic research. Biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin.) highlight an urgent need to explore complementary SST proxies for these cool-water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (δ44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin.) is related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.02)‰ per 1°C, highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C associated with salinities below 33.0 (±0.5)‰, a prominent shift in biomineralization affects the δ44/40Ca of genotyped and core-top N. pachyderma (sin.), becoming insensitive to temperature. These findings highlight the need of more systematic calibration studies on single planktonic foraminiferal species in order to unravel species-specific factors influencing the temperature sensitivity of Ca isotope fractionation and to validate the proxies' applicability
High-resolution spectroscopy of triplet states of Rb2 by femtosecond pump-probe photoionization of doped helium nanodroplets
The dynamics of vibrational wave packets in triplet states of rubidium dimers
(Rb2) formed on helium nanodroplets are studied using femtosecond pump-probe
photoionization spectroscopy. Due to fast desorption of the excited Rb2
molecules off the droplets and due to their low internal temperature, wave
packet oscillations can be followed up to very long pump-probe delay times
>1.5ns. In the first excited triplet state (1)^3\Sigma_g^+, full and fractional
revivals are observed with high contrast. Fourier analysis provides
high-resolution vibrational spectra which are in excellent agreement with ab
initio calculations
PYRAMIR: Calibration and operation of a pyramid near-infrared wavefront sensor
The concept of pyramid wavefront sensors (PWFS) has been around about a
decade by now. However, there is still a great lack of characterizing
measurements that allow the best operation of such a system under real life
conditions at an astronomical telescope. In this article we, therefore,
investigate the behavior and robustness of the pyramid infrared wavefront
sensor PYRAMIR mounted at the 3.5 m telescope at the Calar Alto Observatory
under the influence of different error sources both intrinsic to the sensor,
and arising in the preceding optical system. The intrinsic errors include
diffraction effects on the pyramid edges and detector read out noise. The
external imperfections consist of a Gaussian profile in the intensity
distribution in the pupil plane during calibration, the effect of an optically
resolved reference source, and noncommon-path aberrations. We investigated the
effect of three differently sized reference sources on the calibration of the
PWFS. For the noncommon-path aberrations the quality of the response of the
system is quantified in terms of modal cross talk and aliasing. We investigate
the special behavior of the system regarding tip-tilt control. From our
measurements we derive the method to optimize the calibration procedure and the
setup of a PWFS adaptive optics (AO) system. We also calculate the total
wavefront error arising from aliasing, modal cross talk, measurement error, and
fitting error in order to optimize the number of calibrated modes for on-sky
operations. These measurements result in a prediction of on-sky performance for
various conditions
Lucky Imaging survey for southern M dwarf binaries
While M dwarfs are the most abundant stars in the Milky Way, there is still
large uncertainty about their basic physical properties (mass, luminosity,
radius, etc.) as well as their formation environment. Precise knowledge of
multiplicity characteristics and how they change in this transitional mass
region, between Sun-like stars on the one side and very low mass stars and
brown dwarfs on the other, provide constraints on low mass star and brown dwarf
formation. In the largest M dwarf binary survey to date, we search for
companions to active, and thus preferentially young, M dwarfs in the solar
neighbourhood. We study their binary/multiple properties, such as the
multiplicity frequency and distributions of mass ratio and separation, and
identify short period visual binaries, for which orbital parameters and hence
dynamical mass estimates can be derived in the near future. The observations
are carried out in the SDSS i' and z' band using the Lucky Imaging camera
AstraLux Sur at the ESO 3.5 m New Technology Telescope. In the first part of
the survey, we observed 124 M dwarfs of integrated spectral types M0-M6 and
identified 34 new and 17 previously known companions to 44 stars. We derived
relative astrometry and component photometry for these systems. More than half
of the binaries have separations smaller than 1 arcsec and would have been
missed in a simply seeing-limited survey. Correcting our sample for selection
effects yields a multiplicity fraction of 32+/-6% for 108 M dwarfs within 52 pc
and with angular separations of 0.1-6.0 arcsec, corresponding to projected
separation 3-180 AU at median distance 30 pc. Compared to early-type M dwarfs
(M>0.3M_Sun), later type (and hence lower mass) M dwarf binaries appear to have
closer separations, and more similar masses.Comment: 18 pages, 9 figures. Minor corrections and changes. Revised to match
accepted A&A versio
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