35 research outputs found
Gaia Photometric Science Alerts Crossmatch with Gaia DR3 - Feb. 2024
No full text<p>The <a href="http://gsaweb.ast.cam.ac.uk/alerts/home">Gaia Photometric Science Alerts</a> were crossmatched to the Gaia DR3 catalog on <strong>February 23rd, 2024</strong>. We assumed a 1" separation for each crossmatch. The crossmatch was conducted using the <a href="https://lsdb.readthedocs.io/en/latest/">Large Survey Database</a> (LSDB). </p>
The effect of push-pull rod on the dynamic behavior of movable bridges
No full textIn the Netherlands the design of a movable bridge and machinery part is based on the design standard NEN 6786:2001 (2001). When the bridge is in motion the calculations for the machinery part focus on the dynamic loads (torque) generating at the motor shaft. The calculation of these loads is carried out using tabulated formulas of the standard, which have been derived via a 2-DoF linear dynamic model. In this model the linear spring represents the total stiffness of the machinery part. For the calculation of the spring stiffness the push-pull rod component is excluded, assuming it as a rigid component of the system during the movement cycle of the bridge. The push-pull rod (also known as the buffer) is a component of the machinery of several bascule bridges that connects the leaf of the bridge with the drive mechanism. It consists of stacked disc springs and its stiffness varies based on the load acting on it.The main objectives of this thesis are to model the force deformation behavior of the buffer component, incorporate it in an update set of equations of motion of the bridge-machinery system, and study its effect on the decisive dynamic loads generated at the motor shaft during motion. First, the generalized force deformation diagram of the buffer is formulated with a piecewise function that is based on the force-deflection function for a stack of disc springs according to the standard DIN 2092:2006:03 (2006). Second, the damping of the buffer is modeled as Coulomb friction type, since friction is generated in various position in the stack of disc springs and is the main source of energy dissipation of the buffer component. The validity of the proposed modeling of the buffer component is evaluated via a SDoF model of it, performing a series of dynamic analyses and interpreting the results. Afterwards, the model of the buffer component is introduced in a new set of equations of motion for the bridge-machinery system, derived with the Lagrangian formalism technique. The resulting highly nonlinear set of equations of motion is implemented in the bascule bridge of the new Ramspol bridge located on N50. The analyses aim to the calculation of the torque generated at the motor shaft during an emergency stop at full speed. This loading case is the most decisive with respect to loads generating at the motor shaft.The resulted maximum torque from the dynamic analyses is compared with the torque calculated with the formulas of the standard NEN 6786:2001 (2001). The state of the buffer determines by which formula of the standard the comparison is carried out. A series of dynamic analyses is performed varying, the type of brake (constant or bilinear), the time the brake is applied, the duration of the emergency stop and the friction coefficient of the buffer. In case the buffer is not fully compressed, the calculations with the dynamic model result in lower maximum torque compared with the one according to the standard. In case the buffer is fully compressed the magnitude of the resulting maximum torque depends on the aforementioned variables, whilst the one calculated with the standard is independent of them. In general, the resulting maximum torque derived from the dynamic model decreases with the increase of the friction coefficient of the buffer and the bilinear modeling of the braking.Civil Engineering | Structural Engineerin
Gaia17bpp: A Giant Star with the Deepest and Longest Known Dimming Event
No full textWe report the serendipitous discovery of Gaia17bpp/2MASS J19372316+1759029, a binary star with a deep single large-amplitude dimming event of ∼4.5 mag that lasted over 6.5 yr. Using the optical-to-IR spectral energy distribution (SED), we constrain the primary star to be a cool giant M0III star with effective temperature T _eff = 3850 K and radius R = 58 R _⊙ . Based on the SED fitting, we obtained a bimodal posterior distribution of primary stellar masses with a stronger preference for a 1.5 M _⊙ mass star. Within the last 66 yr of photometric coverage, no other significant dimming events of this depth and duration were identified in the optical light curves. Using a Gaussian process, we fit a generalized Gaussian distribution to the optical and IR light curves and conclude that the dimming event exhibits moderate asymmetries from optical to IR. At the minimum of the dimming event, the Wide-field Infrared Survey Explorer color (W1–W2) differed by ∼0.2 mag relative to the primary star color outside the dimming event. The ingress and egress colors show a shallow reddening profile. We suggest that the main culprit of the dimming event is likely due to the presence of a large, optically thick disk transiting the primary giant star. By fitting a monochromatic transit model of an oblate disk transiting a star, we found good agreement with a slow-moving (0.005 km s ^−1 ) disk with a ∼1.4 au radius. We propose that Gaia17bpp belongs to a rare binary star population similar to the ϵ Aurigae system, which consists of a secondary star enshrouded by an optically thick debris disk
A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients
No full textHo, Anna Y. Q. et al.--Full list of authors: Ho, Anna Y. Q.; Perley, Daniel A.; Gal-Yam, Avishay; Lunnan, Ragnhild; Sollerman, Jesper; Schulze, Steve; Das, Kaustav K.; Dobie, Dougal; Yao, Yuhan; Fremling, Christoffer; Adams, Scott; Anand, Shreya; Andreoni, Igor; Bellm, Eric C.; Bruch, Rachel J.; Burdge, Kevin B.; Castro-Tirado, Alberto J.; Dahiwale, Aishwarya; De, Kishalay; Dekany, Richard; Drake, Andrew J.; Duev, Dmitry A.; Graham, Matthew J.; Helou, George; Kaplan, David L.; Karambelkar, Viraj; Kasliwal, Mansi M.; Kool, Erik C.; Kulkarni, S. R.; Mahabal, Ashish A.; Medford, Michael S.; Miller, A. A.; Nordin, Jakob; Ofek, Eran; Petitpas, Glen; Riddle, Reed; Sharma, Yashvi; Smith, Roger; Stewart, Adam J.; Taggart, Kirsty; Tartaglia, Leonardo; Tzanidakis, Anastasios; Winters, Jan MartinWe present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 day < t1/2 < 12 days, of which 28 have blue (g − r ≲ −0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had predominantly featureless spectra and luminous radio emission: AT2018lug (The Koala) and AT2020xnd (The Camel). Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad Hα in emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (eight) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 24 of the transients. All X-ray and radio observations resulted in nondetections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs and use ZTF's SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate. © 2023. The Author(s). Published by the American Astronomical Society.A.G.Y.'s research is supported by the EU via ERC grant No. 725161, the ISF GW excellence center, an IMOS space infrastructure grant, and BSF/Transformative and GIF grants, as well as The Benoziyo Endowment Fund for the Advancement of Science, the Deloro Institute for Advanced Research in Space and Optics, The Veronika A. Rabl Physics Discretionary Fund, Minerva, Yeda-Sela, and the Schwartz/Reisman Collaborative Science Program; A.G.Y. is the recipient of the Helen and Martin Kimmel Award for Innovative Investigation. R.L. acknowledges support from a Marie Skłodowska-Curie Individual Fellowship within the Horizon 2020 European Union (EU) Framework Programme for Research and Innovation (H2020-MSCA-IF-2017-794467). D.K. is supported by NSF grant AST-1816492. E.C.K. acknowledges support from the G.R.E.A.T research environment funded by Vetenskapsrådet, the Swedish Research Council, under project No. 2016–06012, and support from The Wenner-Gren Foundations. A.A.M. is funded by the Large Synoptic Survey Telescope Corporation (LSSTC), the Brinson Foundation, and the Moore Foundation in support of the LSSTC Data Science Fellowship Program; he also receives support as a CIERA Fellow by the CIERA Postdoctoral Fellowship Program (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University). E.O.O. acknowledges support from the Israeli Science Foundation, The Israeli Ministry of Science, The Bi-National Science foundation, and Minerva. A.J.C.T. acknowledges Y.-D. Hu and A. F. Azamat for their assistance regarding the GTC observation. L.T. acknowledges support from MIUR (PRIN 2017 grant 20179ZF5KS).Peer reviewe
A Disk Origin for the Monoceros Ring and A13 Stellar Overdensities
No full textThe Monoceros Ring (also known as the Galactic Anticenter Stellar Structure) and A13 are stellar overdensities at estimated heliocentric distances of d ̃ 11 kpc and 15 kpc observed at low Galactic latitudes toward the anticenter of our Galaxy. While these overdensities were initially thought to be remnants of a tidally disrupted satellite galaxy, an alternate scenario is that they are composed of stars from the Milky Way (MW) disk kicked out to their current location due to interactions between a satellite galaxy and the disk. To test this scenario, we study the stellar populations of the Monoceros Ring and A13 by measuring the number of RR Lyrae and M giant stars associated with these overdensities. We obtain low-resolution spectroscopy for RR Lyrae stars in the two structures and measure radial velocities to compare with previously measured velocities for M giant stars in the regions of the Monoceros Ring and A13, to assess the fraction of RR Lyrae to M giant stars (f RR:MG) in A13 and Mon/GASS. We perform velocity modeling on 153 RR Lyrae stars (116 in the Monoceros Ring and 37 in A13) and find that both structures have very low f RR:MG. The results support a scenario in which stars in A13 and Mon/GASS formed in the MW disk. We discuss a possible association between Mon/GASS, A13, and the Triangulum-Andromeda overdensity based on their similar velocity distributions and f RR:MG
The large-scale environment of thermonuclear and core-collapse supernovae
No full textThe new generation of wide-field time-domain surveys has made it feasible to study the clustering of supernova (SN) host galaxies in the large-scale structure (LSS) for the first time. We investigate the LSS environment of SN populations, using 106 dark matter density realisations with a resolution of ∼3.8 Mpc, constrained by the 2M+ + galaxy survey. We limit our analysis to redshift z < 0.036, using samples of 498 thermonuclear and 782 core-collapse SNe from the Zwicky Transient Facility’s Bright Transient Survey and Census of the Local Universe catalogues. We detect clustering of SNe with high significance; the observed clustering of the two SNe populations is consistent with each other. Further, the clustering of SN hosts is consistent with that of the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Survey DR12 spectroscopic galaxy sample in the same redshift range. Using a tidal shear classifier, we classify the LSS into voids, sheets, filaments, and knots. We find that both SNe and SDSS galaxies are predominantly found in sheets and filaments. SNe are significantly under-represented in voids and over-represented in knots compared to the volume fraction in these structures. This work opens the potential for using forthcoming wide-field deep SN surveys as a complementary LSS probe.</p
GROWTH on S190814bv: Deep Synoptic Limits on the Optical/Near-Infrared Counterpart to a Neutron Star-Black Hole Merger
No full textOn 2019 August 14, the Advanced LIGO and Virgo interferometers detected the high-significance gravitational wave (GW) signal S190814bv. The GW data indicated that the event resulted from a neutron star–black hole (NSBH) merger, or potentially a low-mass binary BH merger. Due to the low false-alarm rate and the precise localization (23 deg2 at 90%), S190814bv presented the community with the best opportunity yet to directly observe an optical/near-infrared counterpart to an NSBH merger. To search for potential counterparts, the GROWTH Collaboration performed real-time image subtraction on six nights of public Dark Energy Camera images acquired in the 3 weeks following the merger, covering >98% of the localization probability. Using a worldwide network of follow-up facilities, we systematically undertook spectroscopy and imaging of optical counterpart candidates. Combining these data with a photometric redshift catalog, we ruled out each candidate as the counterpart to S190814bv and placed deep, uniform limits on the optical emission associated with S190814bv. For the nearest consistent GW distance, radiative transfer simulations of NSBH mergers constrain the ejecta mass of S190814bv to be M_(ej) < 0.04 M⊙ at polar viewing angles, or M_(ej) < 0.03 M⊙ if the opacity is κ < 2 cm²g⁻¹. Assuming a tidal deformability for the NS at the high end of the range compatible with GW170817 results, our limits would constrain the BH spin component aligned with the orbital momentum to be χ < 0.7 for mass ratios Q < 6, with weaker constraints for more compact NSs
Constraining the Kilonova Rate with Zwicky Transient Facility Searches Independent of Gravitational Wave and Short Gamma-Ray Burst Triggers
No full textThe first binary neutron star merger, GW170817, was accompanied by a radioactivity-powered optical/infrared transient called a kilonova. To date, no compelling kilonova has been found in all-sky optical surveys, independently of short gamma-ray burst and gravitational-wave triggers. In this work, we searched the first 23 months of the Zwicky Transient Facility (ZTF) data stream for candidate kilonovae in the form of rapidly evolving transients. We combined ZTF alert queries with forced point-spread-function photometry and nightly flux stacking to increase our sensitivity to faint and fast transients. Automatic queries yielded >11,200 candidates, 24 of which passed quality checks and selection criteria based on a grid of kilonova models tailored for both binary neutron star and neutron star-black hole mergers. None of the candidates in our sample was deemed a possible kilonova after thorough vetting. The sources that passed our selection criteria are dominated by Galactic cataclysmic variables. We identified two fast transients at high Galactic latitude, one of which is the confirmed afterglow of long-duration GRB 190106A, the other is a possible cosmological afterglow. Using a survey simulation code, we constrained the kilonova rate for a range of models including top-hat, linearly decaying light curves, and synthetic light curves obtained with radiative transfer simulations. For prototypical GW170817-like kilonovae, we constrain the rate to be Gpc-3 yr-1 (95% confidence). By assuming a population of kilonovae with the same geometry and composition of GW170817 observed under a uniform viewing angle distribution, we obtained a constraint on the rate of R < 4029 Gpc-3 yr-1. © 2020. The American Astronomical Society
AT2019wxt: An ultra-stripped supernova candidate discovered in electromagnetic follow-up of a gravitational wave trigger
No full textWe present optical, radio and X-ray observations of a rapidly-evolving
transient AT2019wxt (PS19hgw), discovered during the search for an
electromagnetic (EM) counterpart to the gravitational-wave (GW) trigger
S191213g (LIGO Scientific Collaboration & Virgo Collaboration 2019a). Although
S191213g was not confirmed as a significant GW event in the off-line analysis
of LIGO-Virgo data, AT2019wxt remained an interesting transient due its
peculiar nature. The optical/NIR light curve of AT2019wxt displayed a
double-peaked structure evolving rapidly in a manner analogous to currently
know ultra-stripped supernovae (USSNe) candidates. This double-peaked structure
suggests presence of an extended envelope around the progenitor, best modelled
with two-components: i) early-time shock-cooling emission and ii) late-time
radioactive Ni decay. We constrain the ejecta mass of AT2019wxt at
which indicates a significantly stripped
progenitor that was possibly in a binary system. We also followed-up AT2019wxt
with long-term Chandra and Jansky Very Large Array observations spanning
260 days. We detected no definitive counterparts at the location of
AT2019wxt in these long-term X-ray and radio observational campaigns. We
establish the X-ray upper limit at erg cm s
and detect an excess radio emission from the region of AT2019wxt. However,
there is little evidence for SN1993J- or GW170817-like variability of the radio
flux over the course of our observations. A substantial host galaxy
contribution to the measured radio flux is likely. The discovery and early-time
peak capture of AT2019wxt in optical/NIR observation during EMGW follow-up
observations highlights the need of dedicated early, multi-band photometric
observations to identify USSNe.Comment: 20 pages, 14 figures, Submitted to Ap
GROWTH on S190814bv: Deep Synoptic Limits on the Optical/Near-infrared Counterpart to a Neutron Star-Black Hole Merger
No full textOn 2019 August 14, the Advanced LIGO and Virgo interferometers detected the high-significance gravitational wave (GW) signal S190814bv. The GW data indicated that the event resulted from a neutron star-black hole (NSBH) merger, or potentially a low-mass binary BH merger. Due to the low false-alarm rate and the precise localization (23 deg2 at 90%), S190814bv presented the community with the best opportunity yet to directly observe an optical/near-infrared counterpart to an NSBH merger. To search for potential counterparts, the GROWTH Collaboration performed real-time image subtraction on six nights of public Dark Energy Camera images acquired in the 3 weeks following the merger, covering >98% of the localization probability. Using a worldwide network of follow-up facilities, we systematically undertook spectroscopy and imaging of optical counterpart candidates. Combining these data with a photometric redshift catalog, we ruled out each candidate as the counterpart to S190814bv and placed deep, uniform limits on the optical emission associated with S190814bv. For the nearest consistent GW distance, radiative transfer simulations of NSBH mergers constrain the ejecta mass of S190814bv to be M ej < 0.04 M o ̇ at polar viewing angles, or M ej < 0.03 M o ̇ if the opacity is κ < 2 cm2g-1. Assuming a tidal deformability for the NS at the high end of the range compatible with GW170817 results, our limits would constrain the BH spin component aligned with the orbital momentum to be χ < 0.7 for mass ratios Q < 6, with weaker constraints for more compact NSs. © 2020. The American Astronomical Society
