11,262 research outputs found
325 MHz VLA Observations of Ultracool Dwarfs TVLM 513-46546 and 2MASS J0036+1821104
We present 325 MHz (90 cm wavelength) radio observations of ultracool dwarfs
TVLM 513-46546 and 2MASS J0036+1821104 using the Very Large Array (VLA) in June
2007. Ultracool dwarfs are expected to be undetectable at radio frequencies,
yet observations at 8.5 GHz (3.5 cm) and 4.9 GHz (6 cm) of have revealed
sources with > 100 {\mu}Jy quiescent radio flux and > 1 mJy pulses coincident
with stellar rotation. The anomalous emission is likely a combination of
gyrosynchrotron and cyclotron maser processes in a long-duration, large-scale
magnetic field. Since the characteristic frequency for each process scales
directly with the magnetic field magnitude, emission at lower frequencies may
be detectable from regions with weaker field strength. We detect no significant
radio emission at 325 MHz from TVLM 513-46546 or 2MASS J0036+1821104 over
multiple stellar rotations, establishing 2.5{\sigma} total flux limits of 795
{\mu}Jy and 942 {\mu}Jy respectively. Analysis of an archival VLA 1.4 GHz
observation of 2MASS J0036+1821104 from January 2005 also yields a
non-detection at the level of < 130 {\mu}Jy . The combined radio observation
history (0.3 GHz to 8.5 GHz) for these sources suggests a continuum emission
spectrum for ultracool dwarfs which is either flat or inverted below 2-3 GHz.
Further, if the cyclotron maser instability is responsible for the pulsed radio
emission observed on some ultracool dwarfs, our low-frequency non-detections
suggest that the active region responsible for the high-frequency bursts is
confined within 2 stellar radii and driven by electron beams with energies less
than 5 keV.Comment: 11 pages, 5 figures, submitted to A
Short-Term H-alpha Variability in M Dwarfs
We spectroscopically study the variability of H-alpha emission in mid- to
late-M dwarfs on timescales of ~0.1-1 hr as a proxy for magnetic variability.
About 80% of our sample exhibits statistically significant variability on the
full range of timescales probed by the observations, and with amplitude ratios
in the range of ~1.2-4. No events with an order of magnitude increase in
H-alpha luminosity were detected, indicating that their rate is < 0.05 /hr (95%
confidence level). We find a clear increase in variability with later spectral
type, despite an overall decrease in H-alpha "activity" (i.e.,
L_{H-alpha}/L_{bol}). For the ensemble of H-alpha variability events, we find a
nearly order of magnitude increase in the number of events from timescales of
about 10 to 30 min, followed by a roughly uniform distribution at longer
durations. The event amplitudes follow an exponential distribution with a
characteristic scale of Max(EW)/Min(EW)}-1 ~ 0.7. This distribution predicts a
low rate of ~ 10^{-6} /hr for events with (Max(EW)/Min(EW) > 10, but
serendipitous detections of such events in the past suggests that they
represent a different distribution. Finally, we find a possible decline in the
amplitude of events with durations of > 0.5 hr, which may point to a typical
energy release in H-alpha events for each spectral type (E_{H-alpha} ~
L_{H-alpha} x t ~ const). Longer observations of individual active objects are
required to further investigate this possibility. Similarly, a larger sample
may shed light on whether H-alpha variability correlates with properties such
as age or rotation velocity.Comment: Accepted for publication in Ap
Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. III. X-ray, Radio, and H-alpha Activity Trends in M and L Dwarfs
[Abridged] As part of our on-going investigation into the magnetic field
properties of ultracool dwarfs, we present simultaneous radio, X-ray, and
H-alpha observations of three M9.5-L2.5 dwarfs (BRI0021-0214,
LSR060230.4+391059, and 2MASSJ052338.2-140302). We do not detect X-ray or radio
emission from any of the three sources, despite previous detections of radio
emission from BRI0021 and 2M0523-14. Steady and variable H-alpha emission are
detected from 2M0523-14 and BRI0021, respectively, while no H-alpha emission is
detected from LSR0602+39. Overall, our survey of nine M8-L5 dwarfs doubles the
number of ultracool dwarfs observed in X-rays, and triples the number of L
dwarfs, providing in addition the deepest limits to date, log(L_X/L_bol)<-5.
With this larger sample we find the first clear evidence for a substantial
reduction in X-ray activity, by about two orders of magnitude, from mid-M to
mid-L dwarfs. We find that the decline in both X-rays and H-alpha roughly
follows L_{X,Halpha}/L_bol ~ 10^[-0.4x(SP-M6)] for SP>M6. In the radio band,
however, the luminosity remains relatively unchanged from M0 to L4, leading to
a substantial increase in L_rad/L_bol. Our survey also provides the first
comprehensive set of simultaneous radio/X-ray/H-alpha observations of ultracool
dwarfs, and reveals a clear breakdown of the radio/X-ray correlation beyond
spectral type M7, evolving smoothly from L_{\nu,rad}/L_X ~ 10^-15.5 to
~10^-11.5 Hz^-1 over the narrow spectral type range M7-M9. This breakdown
reflects the substantial reduction in X-ray activity beyond M7, but its
physical origin remains unclear since, as evidenced by the uniform radio
emission, there is no drop in the field dissipation and particle acceleration
efficiency.Comment: Submitted to ApJ; 19 pages, 10 figures, 5 table
Periodic Radio and H-alpha Emission from the L Dwarf Binary 2MASSW J0746425+200032: Exploring the Magnetic Field Topology and Radius of an L Dwarf
[Abridged] We present an 8.5-hour simultaneous radio, X-ray, UV, and optical
observation of the L dwarf binary 2MASSW J0746+20. We detect strong radio
emission, dominated by short-duration periodic pulses at 4.86 GHz with
P=124.32+/-0.11 min. The stability of the pulse profiles and arrival times
demonstrates that they are due to the rotational modulation of a B~1.7 kG
magnetic field. A quiescent non-variable component is also detected, likely due
to emission from a uniform large-scale field. The H-alpha emission exhibits
identical periodicity, but unlike the radio pulses it varies sinusoidally and
is offset by exactly 1/4 of a phase. The sinusoidal variations require
chromospheric emission from a large-scale field structure, with the radio
pulses likely emanating from the magnetic poles. While both light curves can be
explained by a rotating mis-aligned magnetic field, the 1/4 phase lag rules out
a symmetric dipole topology since it would result in a phase lag of 1/2
(poloidal field) or zero (toroidal field). We therefore conclude that either
(i) the field is dominated by a quadrupole configuration, which can naturally
explain the 1/4 phase lag; or (ii) the H-alpha and/or radio emission regions
are not trivially aligned with the field. Regardless of the field topology, we
use the measured period along with the known rotation velocity (vsini=27 km/s),
and the binary orbital inclination (i=142 deg), to derive a radius for the
primary star of 0.078+/-0.010 R_sun. This is the first measurement of the
radius of an L dwarf, and along with a mass of 0.085+/-0.010 M_sun it provides
a constraint on the mass-radius relation below 0.1 M_sun. We find that the
radius is about 30% smaller than expected from theoretical models, even for an
age of a few Gyr.Comment: Submitted to Ap
Short Gamma Ray Bursts: a bimodal origin?
Short-hard Gamma Ray Bursts (SGRBs) are currently thought to arise from
gravitational wave driven coalescences of double neutron star systems forming
either in the field or dynamically in globular clusters. For both channels we
fit the peak flux distribution of BATSE SGRBs to derive the local burst
formation rate and luminosity function. We then compare the resulting redshift
distribution with Swift 2-year data, showing that both formation channels are
needed in order to reproduce the observations. Double neutron stars forming in
globular clusters are found to dominate the distribution at z<0.3, whereas the
field population from primordial binaries can account for the high-z SGRBs.
This result is not in contradiction with the observed host galaxy type of
SGRBs.Comment: 5 pages, 2 figures, accepted for publication in MNRA
The bright optical afterglow of the nearby gamma-ray burst of 29 March 2003
Many past studies of cosmological gamma-ray bursts (GRBs) have been limited
because of the large distance to typical GRBs, resulting in faint afterglows.
There has long been a recognition that a nearby GRB would shed light on the
origin of these mysterious cosmic explosions, as well as the physics of their
fireballs. However, GRBs nearer than z=0.2 are extremely rare, with an
estimated rate of localisation of one every decade. Here, we report the
discovery of bright optical afterglow emission from GRB 030329. Our prompt
dissemination and the brilliance of the afterglow resulted in extensive
followup (more than 65 telescopes) from radio through X-ray bands, as well as
measurement of the redshift, z=0.169. The gamma-ray and afterglow properties of
GRB 030329 are similar to those of cosmological GRBs (after accounting for the
small distance), making this the nearest known cosmological GRB. Observations
have already securely identified the progenitor as a massive star that exploded
as a supernova, and we anticipate futher revelations of the GRB phenomenon from
studies of this source.Comment: 13 pages, 4 figures. Original tex
Closed-loop recycling of rare liquid samples for gas-phase experiments
Many samples of current interest in molecular physics and physical chemistry exist in the liquid phase and are vaporized for use in gas cells, diffuse gas targets, or molecular gas jets. For some of these techniques, the large sample consumption is a limiting factor. When rare, expensive molecules such as custom-made chiral molecules or species with isotopic labels are used, wasting them in the exhaust line of the pumps is quite an expensive and inefficient approach. Therefore, we developed a closed-loop recycling system for molecules with vapor pressures below atmospheric pressure. Once filled, only a few valves have to be adjusted, and a cold trap must be moved after each phase of recycling. The recycling efficiency per turn exceeds 95%
Magnetic properties of G-band bright points in a sunspot moat
We present simultaneous spectropolarimetric observations of four visible and
three infrared spectral lines from the VTT (Tenerife), together with
speckle-reconstructed filtergrams in the G band and the CaII H line core from
the DOT (La Palma). After alignment of the data sets, we used the G-band
intensity to locate bright points (BPs) in the moat of a regular sunspot. With
the cospatial and cotemporal information provided by the polarimetric data, we
characterize the magnetic, kinematic, and thermal properties of the BPs. We
find that (a) 94 % of the BPs are associated with magnetic fields; (b) their
field strengths range between 500 and 1400 G, with a rather flat distribution;
(c) the contrast of BPs in the G band depends on the angle between the vector
magnetic field and the line of sight; (d) the BPs harbor downflows of
magnetized plasma and exhibit Stokes V profiles with large area and amplitude
asymmetries; (e) the magnetic interior of BPs is hotter than the immediate
field-free surroundings by about 1000 K at equal optical depth; and (f) the
mean effective diameter of BPs in our data set is 150 km, with very few BPs
larger than 300 km. Most of these properties can be explained by the classical
magnetic flux tube model. However, the wide range of BP parameters found in
this study indicates that not all G-band BPs are identical to stable long-lived
flux tubes or sheets of kG strength.Comment: Accepted in A&A, 20 pages, 21 figures in main text, 6 fig. in the
Appendices, 3 figures as jpg (fig. 5, C1, C2
Investigating emotion regulation and social information processing as mechanisms linking adverse childhood experiences with psychosocial functioning in young swiss adults: the FACE epidemiological accelerated cohort study.
BACKGROUND
Adverse childhood experiences increase the risk for psychological disorders and lower psychosocial functioning across the lifespan. However, less is known about the processes through which ACE are linked to multiple negative outcomes. The aim of the FACE epidemiological study is to investigate emotion regulation (emotional reactivity, perseverative thinking and self-efficacy for managing emotions) and social information processing (rejection sensitivity, interpretation biases and social understanding) as potential mechanisms linking adverse childhood experiences and psychosocial functioning in a large population sample of young adults. It is embedded in a larger project that also includes an ecological momentary assessment of emotion regulation and social information processing and informs the development and evaluation of an online self-help intervention for young adults with a history of ACE.
METHODS
The study plans to recruit 5000 young adults aged 18 to 21 from the German-speaking Swiss population. Addresses are provided by Swiss Federal Statistical Office and participants are invited by mail to complete a self-report online survey. If the targeted sample size will not be reached, a second additional sample will be recruited via educational facilities such as universities or teacher training colleges or military training schools. Three follow-ups are planned after 1Â year, 2Â years and 3Â years, resulting in ages 18-24 being covered. The main exposure variable is self-reported adverse childhood experiences before the age of 18, measured at the baseline. Primary outcomes are psychosocial functioning across the study period. Secondary outcomes are social information processing, emotion regulation and health care service use. Statistical analyses include a range of latent variable models to identify patterns of adverse childhood experiences and patterns and trajectories of psychosocial adaptation.
DISCUSSION
The results will contribute to the understanding of the underlying mechanisms that link ACE with psychosocial functioning which is crucial for an improved insight into risk and resilience processes and for tailoring interventions. Furthermore, the identification of factors that facilitate or hinder service use among young adults with ACE informs healthcare policies and the provision of appropriate healthcare services.
TRIAL REGISTRATION NUMBER
NCT05122988. The study was reviewed and authorized by the ethical committee of Northwestern and Central Switzerland (BASEC number 2021-01204)
HST and Spitzer Observations of the Host Galaxy of GRB 050904: A Metal-Enriched, Dusty Starburst at z=6.295
We present deep Hubble Space Telescope and Spitzer Space Telescope
observations of the host galaxy of GRB 050904 at z=6.295. The host is detected
in the H-band and marginally at 3.6 micron. From these detections, and limits
in the z'-band and 4.5 micron, we infer an extinction-corrected absolute
magnitude, M(UV)=-20.7 mag, or ~L*, a substantial star formation rate of 15
solar masses per year, and a stellar mass of a few 10^9 solar masses. A
comparison to the published sample of spectroscopically-confirmed galaxies at
z>5.5 reveals that the host of GRB 050904 would evade detection and/or
confirmation in any of the current surveys due to the lack of detectable
Ly-alpha emission, which is likely the result of dust extinction (A[1200]~1.5
mag). This suggests that not all luminous starburst galaxies at z~6 are
currently being accounted for. Most importantly, using the metallicity of
Z~0.05 solar inferred from the afterglow absorption spectrum, our observations
indicate for the first time that the observed evolution in the mass- and
luminosity-metallicity relations from z=0 to z~2 continues on to z>6. The ease
of measuring redshifts and metallicities from the afterglow emission suggests
that in tandem with the next generation ground- and space-based telescopes, a
GRB mission with dedicated near-IR follow-up can provide unique information on
the evolution of stars and galaxies through the epoch of re-ionization.Comment: Submitted to ApJ; 11 pages, 5 figures; A high-resolution version of
figure 1 can be found at http://www.ociw.edu/~eberger/fig1.050904.berger.ep
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