70 research outputs found
Seasonal dynamics and exports of elements from a first‐order 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 concentration–discharge (C‐Q) 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 C‐Q 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 C‐Q 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) C‐Q shapes were observed for dissolved organic carbon and total suspended solids, whereas negative (dilution) C‐Q shapes were observed for most cations (Na+, Mg2+, Ca2+) and biologically cycled anions (NO3−, PO43−, SO42−). Most analytes displayed significant C‐Q 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
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
isochrones we estimated a cluster age of 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 dex. Using this value and the values for the
effective temperatures we determine the reddening to be E mag. Furthermore, we derived the distance to the cluster from Gaia
parallaxes and found 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 Dor and
Scuti members in data from the TESS mission, including the possible
detection of solar-like oscillations in two of the red giants.Comment: 30 pages, 16 figures, accepted for publication in MNRA
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
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
On the need of an ultramassive black hole in OJ 287
The highly variable blazar OJ~287 is commonly discussed as an example of a
binary black hole system. The 130 year long optical light curve is well
explained by a model where the central body is a massive black hole of
18.3510 solar mass that supports a thin accretion disc. The
secondary black hole of 0.1510 solar mass impacts the disc twice
during its 12 year orbit, and causes observable flares. Recently, it has been
argued that an accretion disc with a typical AGN accretion rate and above
mentioned central body mass should be at least six magnitudes brighter than
OJ~287's host galaxy and would therefore be observationally excluded. Based on
the observations of OJ~287's radio jet, detailed in Marscher and Jorstad
(2011), and up-to-date accretion disc models of Azadi et al. (2022), we show
that the V-band magnitude of the accretion disc is unlikely to exceed the host
galaxy brightness by more than one magnitude, and could well be fainter than
the host. This is because accretion power is necessary to launch the jet as
well as to create electromagnetic radiation, distributed across many
wavelengths, and not concentrated especially on the optical V-band. Further, we
note that the claimed V-band concentration of accretion power leads to serious
problems while interpreting observations of other Active Galactic Nuclei.
Therefore, we infer that the mass of the primary black hole and its accretion
rate do not need to be smaller than what is determined in the standard model
for OJ~287
An Earth-sized Planet around an M5 Dwarf Star at 22 pc
We report on the discovery of an Earth-sized transiting planet (R p = 1.015 ± 0.051 R ⊕) in a P = 4.02 day orbit around K2-415 (EPIC 211414619), an M5V star at 22 pc. The planet candidate was first identified by analyzing the light-curve data obtained by the K2 mission, and it is here shown to exist in the most recent data from TESS. Combining the light curves with the data secured by our follow-up observations, including high-resolution imaging and near-infrared spectroscopy with IRD, we rule out false-positive scenarios, finding a low false-positive probability of 2 × 10−4. Based on IRD’s radial velocities of K2-415, which were sparsely taken over three years, we obtain a planet mass of 3.0 ± 2.7 M ⊕ (M p < 7.5 M ⊕ at 95% confidence) for K2-415b. Being one of the lowest-mass stars (≈0.16 M ⊙) known to host an Earth-sized transiting planet, K2-415 will be an interesting target for further follow-up observations, including additional radial velocity monitoring and transit spectroscopy
Hot planets around cool stars -- two short-period mini-Neptunes transiting the late K-dwarf TOI-1260
We present the discovery and characterization of two sub-Neptunes in close
orbits, as well as a tentative outer planet of a similar size, orbiting
TOI-1260 - a low metallicity K6V dwarf star. Photometry from TESS yields radii
of and
, and periods of 3.13 and 7.49 days for TOI-1260b and TOI-1260c,
respectively. We combined the TESS data with a series of ground-based follow-up
observations to characterize the planetary system. From HARPS-N high-precision
radial velocities we obtain
and . The
star is moderately active with a complex activity pattern, which necessitated
the use of Gaussian process regression for both the light curve detrending and
the radial velocity modelling, in the latter case guided by suitable activity
indicators. We successfully disentangle the stellar-induced signal from the
planetary signals, underlining the importance and usefulness of the Gaussian
Process approach. We test the system's stability against atmospheric
photoevaporation and find that the TOI-1260 planets are classic examples of the
structure and composition ambiguity typical for the range
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