97 research outputs found
Seasonal dynamics and exports of elements from a firstâorder stream to a large inland lake in Michigan
Headwater streams are critical components of drainage systems, directly connecting terrestrial and downstream aquatic ecosystems. The amount of water in a stream can alter hydrologic connectivity between the stream and surrounding landscape and is ultimately an important driver of what constituents headwater streams transport. There is a shortage of studies that explore concentrationâdischarge (CâQ) relationships in headwater systems, especially forested watersheds, where the hydrological and ecological processes that control the processing and export of solutes can be directly investigated. We sought to identify the temporal dynamics and spatial patterns of stream chemistry at three points along a forested headwater stream in Northern Michigan and utilize CâQ relationships to explore transport dynamics and potential sources of solutes in the stream. Along the stream, surface flow was seasonal in the main stem, and perennial flow was spatially discontinuous for all but the lowest reaches. Spring snowmelt was the dominant hydrological event in the year with peak flows an order of magnitude larger at the mouth and upper reaches than annual mean discharge. All three CâQ shapes (positive, negative, and flat) were observed at all locations along the stream, with a higher proportion of the analytes showing significant relationships at the mouth than at the mid or upper flumes. At the mouth, positive (flushing) CâQ shapes were observed for dissolved organic carbon and total suspended solids, whereas negative (dilution) CâQ shapes were observed for most cations (Na+, Mg2+, Ca2+) and biologically cycled anions (NO3â, PO43â, SO42â). Most analytes displayed significant CâQ relationships at the mouth, indicating that discharge is a significant driving factor controlling stream chemistry. However, the importance of discharge appeared to decrease moving upstream to the headwaters where more localized or temporally dynamic factors may become more important controls on stream solute patterns.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149221/1/hyp13416.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149221/2/hyp13416_am.pd
PIONIER: a visitor instrument for the VLTI
PIONIER is a 4-telescope visitor instrument for the VLTI, planned to see its
first fringes in 2010. It combines four ATs or four UTs using a pairwise ABCD
integrated optics combiner that can also be used in scanning mode. It provides
low spectral resolution in H and K band. PIONIER is designed for imaging with a
specific emphasis on fast fringe recording to allow closure-phases and
visibilities to be precisely measured. In this work we provide the detailed
description of the instrument and present its updated status.Comment: Proceedings of SPIE conference Optical and Infrared Interferometry II
(Conference 7734) San Diego 201
Solar-like oscillations in Cephei A as seen through SONG and TESS
Fundamental stellar parameters such as mass and radius are some of the most
important building blocks in astronomy, both when it comes to understanding the
star itself and when deriving the properties of any exoplanet(s) they may host.
Asteroseismology of solar-like oscillations allows us to determine these
parameters with high precision. We investigate the solar-like oscillations of
the red-giant-branch star Cep A, which harbours a giant planet on a
wide orbit. We did this by utilising both ground-based radial velocities from
the SONG network and space-borne photometry from the NASA TESS mission. From
the radial velocities and photometric observations, we created a combined power
spectrum, which we used in an asteroseismic analysis to extract individual
frequencies. We clearly identify several radial and quadrupole modes as well as
multiple mixed, dipole modes. We used these frequencies along with
spectroscopic and astrometric constraints to model the star, and we find a mass
of M, a radius of
R, and an age of Gyr. We then used the mass of
Cep A and our SONG radial velocities to derive masses for Cep
B and Cep Ab of M and
M, respectively.Comment: 17 pages, 13 figures, accepted for publication in A&
TOI-1431b/MASCARA-5b: an ultra-hot Jupiter orbiting one of the hottest & brightest known exoplanet host stars
Stars and planetary system
Extremely precise age and metallicity of the open cluster NGC 2506 using detached eclipsing binaries
Accurate stellar parameters of stars in open clusters can help constrain models of stellar structure and evolution. Here, we wish to determine the age and metallicity content of the open cluster NGC 2506. To this end, we investigated three detached eclipsing binaries (DEBs; V2032, V4, and V5) for which we determined their masses and radii, as well as four red giant branch stars for which we determined their effective temperatures, surface gravities, and metallicities. Three of the stars in the DEBs have masses close to the cluster turn-off mass, allowing for extremely precise age determination. Comparing the values for the masses and radii of the binaries to BaSTI (a Bag of Stellar Tracks and Isochrones) isochrones, we estimated a cluster age of 2.01 ± 0.10 Gyr. This does depend on the models used in the comparison, where we have found that the inclusion of convective core-overshooting is necessary to properly model the cluster. From red giant branch stars, we determined values for the effective temperatures, the surface gravities, and the metallicities. From these we find a cluster metallicity of â0.36 ± 0.10 dex. Using this value and the values for the effective temperatures, we determine the reddening to be E(b â y) = 0.057 ± 0.004 mag. Furthermore, we derived the distance to the cluster from Gaia parallaxes and found 3.101 ± 0.017 kpc, and we have performed a radial velocity membership determination for stars in the field of the cluster. Finally, we report on the detection of oscillation signals in Îł Dor and ÎŽ Scuti members in data from the Transiting Exoplanet Survey Satellite (TESS) mission, including the possible detection of solar-like oscillations in two of the red giants.Funding for the Stellar
Astrophysics Centre is provided by The Danish National Research
Foundation (Grant agreement no.: DNRF106). ELS gratefully acknowledges support from the (U.S.) National Science Foundation
under grant AST 1817217. This work has made use of data from
the European Space Agency (ESA) mission Gaia (https://www.
cosmos.esa.int/gaia), processed by the Gaia Data Processing and
Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gai
a/dpac/consortium). Funding for the DPAC has been provided by
national institutions, in particular the institutions participating in
the Gaia Multilateral Agreement. This research has made use of
the VizieR catalogue access tool, CDS, Strasbourg, France
Refining the prediction for OJ 287 next impact flare arrival epoch
The bright blazar OJ~287 routinely parades high brightness bremsstrahlung
flares which are explained as being a result of a secondary supermassive black
hole (SMBH) impacting the accretion disk of a primary SMBH in a binary system.
We begin by showing that these flares occur at times predicted by a simple
analytical formula, based on the Kepler equation, which explains flares since
1888. The next impact flare, namely the flare number 26, is rather peculiar as
it breaks the typical pattern of two impact flares per 12 year cycle. This will
be the third bremsstrahlung flare of the current cycle that follows the already
observed 2015 and 2019 impact flares from OJ~287. Unfortunately, astrophysical
considerations make it difficult to predict the exact arrival epoch of the
flare number 26. In the second part of the paper, we describe our recent OJ~287
observations. They show that the pre-flare light curve of flare number 22,
observed in 2005, exhibits similar activity as the pre-flare light curve in
2022, preceding the expected flare number 26 in our model. We argue that the
pre-flare activity most likely arises in the primary jet whose activity is
modulated by the transit of the secondary SMBH through the accretion disk of
the primary. Observing the next impact flare of OJ~287 in October 2022 will
substantiate the theory of disk impacts in binary black hole systems.Comment: 16 pages, 2 figure
The low density, hot Jupiter TOI-640 b is on a polar orbit
TOI-640 b is a hot, puffy Jupiter with a mass of M
and radius of R, orbiting a slightly evolved F-type
star with a separation of R. Through
spectroscopic in-transit observations made with the HARPS spectrograph, we
measured the Rossiter-McLaughlin effect, analysing both in-transit radial
velocities and the distortion of the stellar spectral lines. From these
observations, we find the host star to have a projected obliquity of
. From the TESS light curve, we measured the stellar
rotation period, allowing us to determine the stellar inclination,
, meaning we are viewing the star pole-on. Combining
this with the orbital inclination allowed us to calculate the host star
obliquity, . TOI-640 b joins a group of planets orbiting
over stellar poles within the range . The origin of this
orbital configuration is not well understood.Comment: 15 pages, 12 figures, accepted for publication in A&A, in pres
Refining the 2022 OJ 287 impact flare arrival epoch
The bright blazar OJ~287 routinely parades high brightness bremsstrahlung
flares, which are explained as being a result of a secondary supermassive black
hole (SMBH) impacting the accretion disc of a more massive primary SMBH in a
binary system. The accretion disc is not rigid but rather bends in a calculable
way due to the tidal influence of the secondary. Below we refer to this
phenomenon as a variable disc level. We begin by showing that these flares
occur at times predicted by a simple analytical formula, based on general
relativity inspired modified Kepler equation, which explains impact flares
since 1888.
The 2022 impact flare, namely flare number 26, is rather peculiar as it
breaks the typical pattern of two impact flares per 12-year cycle. This is the
third bremsstrahlung flare of the current cycle that follows the already
observed 2015 and 2019 impact flares from OJ~287.
It turns out that the arrival epoch of flare number 26 is sensitive to the
level of primary SMBH's accretion disc relative to its mean level in our model.
We incorporate these tidally induced changes in the level of the accretion disc
to infer that the thermal flare should have occurred during July-August 2022,
when it was not possible to observe it from the Earth. Thereafter, we explore
possible observational evidence for certain pre-flare activity by employing
spectral and polarimetric data from our campaigns in 2004/05 and 2021/22. We
point out theoretical and observational implications of two observed
mini-flares during January-February 2022.Comment: 29 pages, 6 figures, 1 table. arXiv admin note: text overlap with
arXiv:2209.0836
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