12 research outputs found
Imprints of Sagittarius accretion event: Young O-rich stars and discontinuous chemical evolution in Milky Way disc
The Milky Way has undergone significant transformations in its early history,
characterised by violent mergers and the accretion of satellite galaxies. Among
these events, the infall of the satellite galaxy Gaia-Enceladus/Sausage is
recognised as the last major merger event, fundamentally altering the evolution
of the Milky Way and shaping its chemo-dynamical structure. However, recent
observational evidence suggests that the Milky Way remains undergone notable
events of star formation in the past 4 Gyr, which is thought to be triggered by
the perturbations from Sagittarius dwarf galaxy (Sgr). Here we report chemical
signatures of the Sgr accretion event in the past 4 Gyr, using the [Fe/H] and
[O/Fe] ratios in the thin disc, which is reported for the first time. It
reveals that the previously discovered V-shape structure of age-[Fe/H] relation
varies across different Galactic locations and has rich substructures.
Interestingly, we discover a discontinuous structure at z 0.3
kpc, interrupted by a recent burst of star formation from 4 Gyr to 2 Gyr ago.
In this episode, we find a significant rise in oxygen abundance leading to a
distinct [O/Fe] gradient, contributing to the formation of young O-rich stars.
Combined with the simulated star formation history and chemical abundance of
Sgr, we suggest that the Sgr is an important actor in the discontinuous
chemical evolution of the Milky Way disc.Comment: 17 pages, 15 figures. Under review at Nature Communication
Characterising abundance-age relations of GALAH stars using oxygen-enhanced stellar models
Main Sequence Turn-off stars (MSTO) and subgiant stars are good tracers of
galactic populations. We present a study of 41,034 MSTO and subgiant stars from
the GALAH survey. Using a grid of stellar models that accounts for the
variation of O abundances, we determine their ages with a median age
uncertainty of 9.4 per cent. Our analysis reveals that the ages of high-O
stars based on O-enhanced models (OEM models) are smaller than those determined
with -enhanced models, resulting in a mean fractional age difference of
-5.3 per cent at [O/] = 0.2 and -11.0 per cent at [O/] = 0.4.
This age difference significantly impacts the age distribution of thick disc
and halo stars, leading to a steeper downward trend in the [Fe/H]-age plane
from 8 Gyr to 14 Gyr, indicating a shorter formation time-scale and a faster
chemical-enhanced history for these populations. We confirm the V-shape of the
normalized age-metallicity distribution ([Fe/H]) of thin disc
stars, which is presumably a consequence of the second gas infall.
Additionally, we find that the halo stars in our sample can be divided into two
sequences, a metal-rich sequence (Splash stars) and a metal-poor sequence
(accreted stars), with the Splash stars predominantly older than 9 Gyr and the
accreted halo stars older than 10 Gyr. Finally, we observe two distinct
sequences in the relations between various chemical abundances and age for disc
stars, namely a young sequence with ages 8 Gyr and an old sequence
with ages 8 Gyr.Comment: 11 pages, 12 figure
Assessing the Ecological Effects of Water Transport to a Lake in Arid Regions: A Case Study of Qingtu Lake in Shiyang River Basin, Northwest China
With the continuous growth of economic water consumption in arid regions, many endorheic rivers and terminal lakes have desiccated. As an important ecological engineering measure, water transport in arid regions has vital ecological significance for protecting the regional ecological environment and delaying desertification. In this study, Qingtu Lake, the terminal lake of Shiyang River, was selected to analyze the ecological effects of water transport by means of remote sensing interpretations and current year field investigations. The results demonstrated that, in July 2018, the water surface had formed and recovered to 5.68 km2. Additionally, Qingtu Lake formed a spatial gradient distribution in groundwater depth. The depth increased in gradient from the waterside to the desert edge. There was a significant increase in the overall regional vegetation coverage, which mainly occurred in the water areas because of the extensive growth in Phragmites australis, which reached 10.54 km2 in area in 2018. Furthermore, the regional vegetation formed a gradient distribution, which transitioned from hygrophytes to xerophytes. This study can provide guidelines for the protection and restoration of lakes in arid regions
High-Temperature-Resistant Fiber Laser Vector Accelerometer Based on a Self-Compensated Multicore Fiber Bragg Grating
We propose and demonstrate a novel high-temperature-resistant vector accelerometer, consisting of a ring cavity laser and sensing probe (i.e., fiber Bragg gratings (FBGs)) inscribed in a seven-core fiber (SCF) by using the femtosecond laser direct writing technique. A ring cavity laser serves as a light source. Three FBGs in the outer cores of SCF, which are not aligned in a straight line, are employed to test the vibration. These three FBGs have 120° angular separation in the SCF, and hence, vibration orientation and acceleration can be measured simultaneously. Moreover, the FBG in the central core was used as a reflector in the ring cavity laser, benefiting to resist external interference factors, such as temperature and strain fluctuation. Such a proposed accelerometer exhibits a working frequency bandwidth ranging from 4 to 68 Hz, a maximum sensitivity of 54.2 mV/g, and the best azimuthal angle accuracy of 0.21° over a range of 0–360°. Furthermore, we investigated the effect of strain and temperature on the performance of this sensor. The signal-to-noise ratio (SNR) only exhibits a fluctuation of ~1 dB in the range (0, 2289 με) and (50 °C, 1050 °C). Hence, such a vector accelerometer can operate in harsh environments, such as in aerospace and a nuclear reactor
Investigating 16 Open Clusters in the Kepler/K2-Gaia DR3 field. I. Membership, Binary, and Rotation
Using data from the Gaia Data Release 3 (Gaia DR3) and Kepler/K2, we present
a catalog of 16 open clusters with ages ranging from 4 to 4000 Myr, which
provides detailed information on membership, binary systems, and rotation. We
assess the memberships in 5D phase space, and estimate the basic parameters of
each cluster. Among the 20,160 members, there are 4,381 stars identified as
binary candidates and 49 stars as blue straggler stars. The fraction of
binaries vary in each cluster, and the range between 9% to 44%. We obtain the
rotation periods of 5,467 members, of which 4,304 are determined in this work.
To establish a benchmark for the rotation-age-color relation, we construct
color-period diagrams. We find that the rotational features of binaries are
similar to that of single stars, while features for binaries are more scattered
in the rotation period. Moreover, the morphology of the color-period
relationship is already established for Upper Scorpius at the age of 19 Myr,
and some stars of varying spectral types (i.e. FG-, K-, and M-type) show
different spin-down rates after the age of ~110 Myr. By incorporating the
effects of stalled spin-down into our analysis, we develop an empirical
rotation-age-color relation, which is valid with ages between 700 - 4000 Myr
and colors corresponding to a range of 0.5 < (G_BP-G_RP)0 < 2.5 mag.Comment: 21 pages, 17 figures, accepted for publication in ApJ
Relations of Rotation and Chromospheric Activity to Stellar Age for FGK Dwarfs from Kepler and LAMOST
The empirical relations between rotation period, chromospheric activity, and age can be used to estimate stellar age. To calibrate these relations, we present a catalog, including the masses and ages of 52,321 FGK dwarfs, 47,489 chromospheric activity index , 6077 rotation periods P _rot , and variability amplitudes S _ph , based on data from LAMOST DR7, Kepler, and Gaia Data Release 3. We find a pronounced correlation among P _rot , age, and [Fe/H] throughout the main-sequence phase for F dwarfs. However, the decrease of over time is not significant except for those with [Fe/H] < −0.1. For G dwarfs, both P _rot and are reliable age probes in the ranges ∼2–11 Gyr and ∼2–13 Gyr, respectively. K dwarfs exhibit a prominent decrease in within the age range of ∼3–13 Gyr when the relation of P _rot – τ is invalid. These relations are very important for promptly estimating the age of a vast number of stars, thus serving as a powerful tool in advancing the fields of exoplanet properties, stellar evolution, and Galactic archeology
Age of FGK Dwarfs Observed with LAMOST and GALAH: Considering the Oxygen Enhancement
Varying oxygen abundance could impact the modeling-inferred ages. This work
aims to estimate the ages of dwarfs considering observed oxygen abundance. To
characterize 67,503 LAMOST and 4,006 GALAH FGK-type dwarf stars, we construct a
grid of stellar models which take into account oxygen abundance as an
independent model input. Compared with ages determined with commonly-used
-enhanced models, we find a difference of 9% on average when the
observed oxygen abundance is considered. The age differences between the two
types of models are correlated to [Fe/H] and [O/], and they are
relatively significant on stars with [Fe/H] -0.6 dex. Generally,
varying 0.2 dex in [O/] will alter the age estimates of metal-rich
(-0.2 [Fe/H] 0.2) stars by 10%, and relatively metal-poor (-1
[Fe/H] -0.2) stars by 15%. Of the low-O stars with [Fe/H] 0.1 dex
and [O/] -0.2 dex, many have fractional age differences of
10%, and even reach up to 27%. The fractional age difference of high-O
stars with [O/] 0.4 dex reaches up to -33% to -42% at [Fe/H]
-0.6 dex. We also analyze the chemical properties of these stars. We
find a decreasing trend of [Fe/H] with age from 7.5-9 Gyr to 5-6.5 Gyr for the
stars from the LAMOST and GALAH. The [O/Fe] of these stars increases with
decreasing age from 7.5-9 Gyr to 3-4 Gyr, indicating that the younger
population is more O-rich.Comment: 18 pages, 12 figures, accepted for publication in ApJ