243 research outputs found
The young open cluster Trumpler 3
We present a photometric and spectroscopic study of the poorly investigated
open cluster Trumpler~3. Basic parameters such as the age of Myr, the
color excess mag, the distance of kpc and
the limiting radius of 12' were redetermined and compared with previous
preliminary studies. The distance of kpc was determined
independently by spectral parallaxes. Simultaneously, our analysis allowed us
to estimate a total number of members to be and a total
mass of the cluster to be . We also
determined a state of cluster's dynamical evolution. We conclude that
Trumpler~3 is a young low-massive stellar ensemble with a typical mass function
slope, located near to the outer edge of the Galaxy's Orion Spur. As a result
of a wide-field search for short period variable stars, 24 variables were
discovered in the cluster's area. Only one of them -- a variable of the
-Dor type -- was found to be a likely cluster member
The Horizontal Ice Nucleation Chamber (HINC) : INP measurements at conditions relevant for mixed-phase clouds at the High Altitude Research Station Jungfraujoch
In this work we describe the Horizontal Ice Nucleation Chamber (HINC) as a new instrument to measure ambient ice-nucleating particle
(INP) concentrations for conditions relevant to mixed-phase
clouds. Laboratory verification and validation experiments confirm
the accuracy of the thermodynamic conditions of temperature (T)
and relative humidity (RH) in HINC with uncertainties in T
of ±0.4 K and in RH with respect to water
(RHw) of ±1.5 %, which translates
into an uncertainty in RH with respect to ice
(RHi) of ±3.0 % at T > 235 K. For further validation of HINC as a field
instrument, two measurement campaigns were conducted in winters 2015
and 2016 at the High Altitude Research Station Jungfraujoch (JFJ;
Switzerland, 3580 m a. s. l. ) to sample ambient INPs. During
winters 2015 and 2016 the site encountered free-tropospheric
conditions 92 and 79 % of the time, respectively. We measured
INP concentrations at 242 K at water-subsaturated conditions
(RHw = 94 %), relevant for the formation of
ice clouds, and in the water-supersaturated regime
(RHw = 104 %) to represent ice formation
occurring under mixed-phase cloud conditions. In winters 2015 and
2016 the median INP concentrations at RHw = 94 % was below the minimum detectable concentration. At
RHw = 104 %, INP concentrations were an
order of magnitude higher, with median concentrations in winter 2015
of 2.8 per standard liter (std L−1; normalized to
standard T of 273 K and pressure, p, of
1013 hPa) and 4.7 std L−1 in winter 2016. The
measurements are in agreement with previous winter measurements
obtained with the Portable Ice Nucleation Chamber (PINC) of
2.2 std L−1 at the same location. During winter 2015,
two events caused the INP concentrations at RHw = 104 % to significantly increase above the campaign
average. First, an increase to 72.1 std L−1 was measured
during an event influenced by marine air, arriving at the JFJ from
the North Sea and the Norwegian Sea. The contribution from
anthropogenic or other sources can thereby not be ruled out. Second,
INP concentrations up to 146.2 std L−1 were observed
during a Saharan dust event. To our knowledge this is the first time
that a clear enrichment in ambient INP concentration in remote
regions of the atmosphere is observed during a time of marine air
mass influence, suggesting the importance of marine particles on ice
nucleation in the free troposphere
The stellar content of the young open cluster Trumpler 37
With an apparent cluster diameter of 1.5{\deg} and an age of ~4 Myr, Trumpler
37 is an ideal target for photometric monitoring of young stars as well as for
the search of planetary transits, eclipsing binaries and other sources of
variability. The YETI consortium has monitored Trumpler 37 throughout 2010 and
2011 to obtain a comprehensive view of variable phenomena in this region. In
this first paper we present the cluster properties and membership determination
as derived from an extensive investigation of the literature. We also compared
the coordinate list to some YETI images. For 1872 stars we found literature
data. Among them 774 have high probability of being member and 125 a medium
probability. Based on infrared data we re-calculate a cluster extinction of
0.9-1.2 mag. We can confirm the age and distance to be 3-5 Myr and ~870 pc.
Stellar masses are determined from theoretical models and the mass function is
fitted with a power-law index of alpha=1.90 (0.1-0.4 M_sun) and alpha=1.12
(1-10 M_sun).Comment: 9 pages, 10 figures, 2 long tables, accepte
A Possible Detection of Occultation by a Proto-planetary Clump in GM Cephei
GM Cep in the young (~4 Myr) open cluster Trumpler 37 has been known to be an
abrupt variable and to have a circumstellar disk with very active accretion.
Our monitoring observations in 2009-2011 revealed the star to show sporadic
flare events, each with brightening of < 0.5 mag lasting for days. These
brightening events, associated with a color change toward the blue, should
originate from an increased accretion activity. Moreover, the star also
underwent a brightness drop of ~1 mag lasting for about a month, during which
the star became bluer when fainter. Such brightness drops seem to have a
recurrence time scale of a year, as evidenced in our data and the photometric
behavior of GM Cep over a century. Between consecutive drops, the star
brightened gradually by about 1 mag and became blue at peak luminosity. We
propose that the drop is caused by obscuration of the central star by an
orbiting dust concentration. The UX Orionis type of activity in GM Cep
therefore exemplifies the disk inhomogeneity process in transition between
grain coagulation and planetesimal formation in a young circumstellar disk.Comment: In submission to the Astrophysical Journal, 4 figure
Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin
The transiting planet WASP-12 b was identified as a potential target for
transit timing studies because a departure from a linear ephemeris was reported
in the literature. Such deviations could be caused by an additional planet in
the system. We attempt to confirm the existence of claimed variations in
transit timing and interpret its origin. We organised a multi-site campaign to
observe transits by WASP-12 b in three observing seasons, using 0.5-2.6-metre
telescopes. We obtained 61 transit light curves, many of them with
sub-millimagnitude precision. The simultaneous analysis of the best-quality
datasets allowed us to obtain refined system parameters, which agree with
values reported in previous studies. The residuals versus a linear ephemeris
reveal a possible periodic signal that may be approximated by a sinusoid with
an amplitude of 0.00068+/-0.00013 d and period of 500+/-20 orbital periods of
WASP-12 b. The joint analysis of timing data and published radial velocity
measurements results in a two-planet model which better explains observations
than single-planet scenarios. We hypothesize that WASP-12 b might be not the
only planet in the system and there might be the additional 0.1 M_Jup body on a
3.6-d eccentric orbit. A dynamical analysis indicates that the proposed
two-planet system is stable over long timescales.Comment: Accepted for publication in A&
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