An official website of the United States government
We reconstructed the star formation history of the Sco-Cen OB association using a novel high-resolution age map of the region. We developed an approach to produce robust ages for Sco-Cen’s recently identified 37 stellar clusters using theSigMAalgorithm. The Sco-Cen star formation timeline reveals four periods of enhanced star formation activity, or bursts, remarkably separated by about 5 Myr. Of these, the second burst, which occurred about 15 million years ago, is by far the dominant one, and most of Sco-Cen’s stars and clusters were in place by the end of this burst. The formation of stars and clusters in Sco-Cen is correlated but not linearly, implying that more stars were formed per cluster during the peak of the star formation rate. Most of the clusters that are large enough to have supernova precursors were formed during the second burst around 15 Myr ago. Star and cluster formation activity has been continuously declining since then. We have clear evidence that Sco-Cen formed from the inside out and that it contains 100-pc long chains of contiguous clusters exhibiting well-defined age gradients, from massive older clusters to smaller young clusters. These observables suggest an important role for feedback in forming about half of Sco-Cen stars, although follow-up work is needed to quantify this statement. Finally, we confirm that the Upper-Sco age controversy discussed in the literature during the last decades is solved: the nine clusters previously lumped together as Upper-Sco, a benchmark region for planet formation studies, exhibit a wide range of ages from 3 to 19 Myr.
more »
« less
The long-term optical activity of the propellers AE Aquarii and AR Scorpii
Abstract This analysis of the long-term optical activity of the propellers AE Aqr and AR Sco uses data from the Catalina Real-time Transient Survey, DASCH, and AAVSO. The site and character of the emissions from the phenomena caused by the magnetic field of the white dwarf (WD) vary from system to system. The histogram of intensities of the ensemble of flares of AE Aqr suggests that the long-term activity consists of a large variety of the peak magnitudes of the flares, with the probability of their detection gradually decreasing with increasing intensity. Any increase of activity only leads to an increase of the number of blobs of the transferring matter. We also detected a season with a transient decrease or even a cessation of the mass outflow from the donor to the lobe of the WD. The very strong orbital modulation of AR Sco is most stable in the phases of the extrema of brightness for about a century; its minor changes suggest that the trailing side of the synchrotron-emitting region is more unstable than the leading side.
more »
« less
- Award ID(s):
- 1910561
- PAR ID:
- 10447773
- Date Published:
- Journal Name:
- Publications of the Astronomical Society of Japan
- Volume:
- 72
- Issue:
- 2
- ISSN:
- 0004-6264
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract With the aim of investigating how the magnetic field in solar active regions (ARs) controls flare activity, i.e., whether a confined or eruptive flare occurs, we analyze 106 flares of Geostationary Operational Environmental Satellite class ≥M1.0 during 2010–2019. We calculate mean characteristic twist parameters α FPIL within the “flaring polarity inversion line” region and α HFED within the area of high photospheric magnetic free energy density, which both provide measures of the nonpotentiality of the AR core region. Magnetic twist is thought to be related to the driving force of electric current-driven instabilities, such as the helical kink instability. We also calculate total unsigned magnetic flux (Φ AR ) of ARs producing the flare, which describes the strength of the background field confinement. By considering both the constraining effect of background magnetic fields and the magnetic nonpotentiality of ARs, we propose a new parameter α /Φ AR to measure the probability for a large flare to be associated with a coronal mass ejection (CME). We find that in about 90% of eruptive flares, α FPIL /Φ AR and α HFED /Φ AR are beyond critical values (2.2 × 10 −24 and 3.2 × 10 −24 Mm −1 Mx −1 ), whereas they are less than critical values in ∼80% of confined flares. This indicates that the new parameter α /Φ AR is well able to distinguish eruptive flares from confined flares. Our investigation suggests that the relative measure of magnetic nonpotentiality within the AR core over the restriction of the background field largely controls the capability of ARs to produce eruptive flares.more » « less
-
Architectural Engineering (AE) programs typically offer programs of study in at least two subdisciplines that relate to building design and construction. AE students may struggle to select a subdiscipline due to their low exposure and engagement with topics that would inform their decision. Previous research indicates that the immersive nature of virtual and augmented reality (VR/AR) can increase students’ engagement and motivation regarding course content and discipline decisions. The purpose of this study was to investigate the impact of a pilot browser-based virtual reality intervention on first-year AE students’ understanding of the AE subdisciplines and choice for future study, with particular attention to demographic subgroup differences. This pilot was a testbed for a larger set of Virtual/Augmented-Reality-Based Discipline Exploration Rotations (VADERs), which are instructional modules that engage students in authentic AE tasks. In Fall 2020, the pilot VADER-1 module was incorporated into first-year AE courses at one R1 university and one R2 historically black university. This module encouraged students to explore AE subdisciplines through the virtual design of a clinic. Pre-post intervention surveys were used to investigate change in students’ understanding of AE and its subdisciplines. Students reported that their subdiscipline understanding increased significantly. Further, 74% of students reported an increase in their confidence in their choice, and over 30% of students changed their top subdiscipline choice. Some slight differences between demographic subgroups were found. VR/AR interventions hold promise for providing AE students with needed exposure to the practice of the discipline and its subdisciplines.more » « less
-
This paper presents Hit2Flux, a machine learning framework for boiling heat flux prediction using acoustic emission (AE) hits generated through threshold-based transient sampling. Unlike continuously sampled data, AE hits are recorded when the signal exceeds a predefined threshold and are thus discontinuous in nature. Meanwhile, each hit represents a waveform at a high sampling frequency ( 1 MHz). In order to capture the features of both the high-frequency waveforms and the temporal distribution of hits, Hit2Flux involves i) feature extraction by transforming AE hits into the frequency domain and organizing these spectra into sequences using a rolling window to form “sequences-of-sequences,” and ii) heat flux prediction using a long short-term memory (LSTM) network with sequences of sequences. The model is trained on AE hits recorded during pool boiling experiments using an AE sensor attached to the boiling chamber. Continuously sampled acoustic data using a hydrophone were also collected as a reference data set for this study. Results demonstrate that the proposed AE-based method achieves performance comparable to hydrophones, validating its potential for heat flux monitoring. Additionally, it is shown that the inclusion of multiple acoustic emission hits as model inputs leads to higher performance. The Hit2Flux model is also compared to methods pairing various signal preparation techniques with state-of-the-art models. This comparison further highlighted the superior accuracy of the proposed approach. The developed Hi2Flux algorithm can be applied to other transient sampling events, such as structural health monitoring, detection of electromagnetic pulses, among others.more » « less
-
Abstract ASASSN-14ko is a recently discovered periodically flaring transient at the center of the active galactic nucleus (AGN) ESO 253−G003 with a slowly decreasing period. Here, we show that the flares originate from the northern, brighter nucleus in this dual-AGN, post-merger system. The light curves for the two flares that occurred in 2020 May and September are nearly identical over all wavelengths. For both events, Swift observations showed that the UV and optical wavelengths brightened in unison. The effective temperature of the UV/optical emission rises and falls with the increase and subsequent decline in the luminosity. The X-ray flux, by contrast, first rapidly drops over ∼2.6 days, rises for ∼5.8 days, drops again over ∼4.3 days, and then recovers. The X-ray spectral evolution of the two flares differ, however. During the 2020 May peak the spectrum softened with increases in the X-ray luminosity, while we observed the reverse for the 2020 September peak. We found a small change in the period derivative, which seems to indicate that the system does not have a static period derivative and there is some stochasticity in its evolution.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/pasj/psaa012
