Ashkbiz Danehkar

Eureka Scientific

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M. S. Oey

University of Michigan–Ann Arbor

Q. A. Parker

University of Hong Kong

William J. Gray

University of Michigan–Ann Arbor

Michael A. Nowak

Washington University in St. Louis

I. Kourakis

Khalifa University of Science and Technology

M. A. Hellberg

University of KwaZulu-Natal

D. J. Frew

European Space Astronomy Centre

Julia C. Lee

Northwestern University

G. A. Kriss

Space Telescope Science Institute

Randall K. Smith

Center for Astrophysics Harvard & Smithsonian

Cooperative Institutions

Center for Astrophysics Harvard & Smithsonian

University of Michigan–Ann Arbor

Macquarie University

Space Telescope Science Institute

Harvard University

Massachusetts Institute of Technology

Stockholm University

University College London

Smithsonian Astrophysical Observatory

University of Craiova

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Electric-Magnetic Duality in Gravity and Higher-Spin Fields

Frontiers in Physics (2019)

Ashkbiz Danehkar

Over the past two decades, electric-magnetic duality has made significant progress in linearized gravity and higher spin gauge fields in arbitrary dimensions. By analogy with Maxwell theory, the Dirac quantization condition has been generalized to both the conserved electric-type and magnetic-type sources associated with gravitational fields and higher spin fields. The linearized Einstein equations in $D$ dimensions, which are expressed in terms of the Pauli-Fierz field of the \textit{graviton} described by a 2nd-rank symmetric tensor, can be dual to the linearized field equations of the \textit{dual graviton} described by a Young symmetry $(D-3, 1)$ tensor. Hence, the dual formulations of linearized gravity are written by a 2nd-rank symmetric tensor describing the Pauli-Fierz field of the dual graviton in $D=4$, while we have the Curtright field with Young symmetry type $(2,1)$ in $D=5$. The equations of motion of spin-$s$ fields ($s>2$) described by the generalized Fronsdal action can also be dualized to the equations of motion of dual spin-$s$ fields. In this review, we focus on dual formulations of gravity and higher spin fields in the linearized theory, and study their SO(2) electric-magnetic duality invariance, twisted self-duality conditions, harmonic conditions for wave solutions, and their configurations with electric-type and magnetic-type sources. Furthermore, we briefly discuss the latest developments in their interacting theories.

Duality (order theory)

Linearized gravity

10.3389/fphy.2018.00146

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Citations (12)

astroneb/WR_PN_Kinematic_Models: WR-PN-Kinematic-Models.1.0

Zenodo (CERN European Organization for Nuclear Research) (2021)

Ashkbiz Danehkar

Morpho-kinematic properties of Wolf-Rayet planetary nebulae. Supplementary Data Figure 5. The interactive figure of the morpho-kinematic mesh models of the PNe M 3-30, Hb 4, IC 1297, Th 2-A, Pe 1-1, M 1-32, M 3-15, M 1-25, Hen 2-142, K 2-16, MGC 6578, M 2-42, NGC 6567 and NGC 6629. Citation

@article{Danehkar2021, author = {{Danehkar}, A.}, title = {Morpho-kinematic properties of Wolf-Rayet planetary nebulae}, journal = {submitted (arXiv:2107.03994)}, volume = {}, number = {}, pages = {}, year = {2021}, doi = {} }

Learn More GitPage: https://astroneb.github.io/WR_PN_Kinematic_Models/

10.5281/zenodo.5393975

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Dual Fields of Massive/Massless Gravitons in IR/UV Completions

Ashkbiz Danehkar Hassan Alshal Thomas Curtright

In the holographic picture, the BEH mechanism in d-dimensional Yang-Mills theories is conjectured to provide a Higgs-like mechanism for gravity in d+1 dimensions, resulting in massive (or massless) gravitons in IR (or UV) completions. Accordingly, one could imagine dual (magnetic-type) fields of massive gravitons in the IR (low-energy) limit that are coupled to the curl of their own energy-momentum, as well as to the rotation of matter fields on large scales. This hypothesis, which might solve cosmological issues currently ascribed to dark matter and dark energy, needs to be examined by the future LISA mission using observations of gravitational waves emitted from extragalactic sources.

Massless particle

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galacticwinds/Catastrophic_Cooling_Superwinds_II_Data: Catastrophic-Cooling-Superwinds-II-Data.1.2

Zenodo (CERN European Organization for Nuclear Research) (2021)

Ashkbiz Danehkar M. S. Oey William J. Gray

Catastrophic Cooling in Superwinds. II. Exploring the Parameter Space, Supplementary Material The files of the interactive figure (64 images) of Figure 2, the interactive animation (64 videos) of Figure 3, the interactive figure (192 images) of Figure 6, and the compressed (tar.gz) file of the 6 machine-readable table files (a portion shown for guidance regarding its form and content in Table 3) are archived on Zenodo. Figure 2. From top to bottom: the interactive figure of the temperature and density profiles of the superwinds on a logarithmic scale. The different regions separated by dotted lines: (a) freely expanding wind, (b) shocked-wind, (c) shell, and (d) ambient medium. The adiabatic temperature and density profile for each model are shown by dashed lines. Figure 3. From top to bottom: the interactive animation of the temperature and density profiles of the superwinds on a logarithmic scale. The different regions separated by dotted lines: (a) freely expanding wind, (b) shocked-wind, (c) shell, and (d) ambient medium. The adiabatic temperature and density profile for each model are shown by dashed lines. Figure 6. Top Panels: The hydrogen temperature profiles (left panels) along with the adiabatic prediction (red dashed line) in the CPI case, and the line emissivities (right panels) of the superwind models on a logarithmic scale, from top to bottom, in the PI and CPI cases. Bottom Panels: The hydrogen density profiles (left panels) along with the adiabatic prediction (red dashed lines), and the ionic fractions (right panels) on a logarithmic scale for the PI and CPI cases. The start and end of the hot bubble (region b), the end of the shell (region c), and the Strömgren radius are shown by dotted, dashed, dash-dotted, and solid lines (gray color), respectively. Table 3. Integrated luminosities (unit in erg/s) from the different ionization models. Citation

@article{Danehkar2021, author = {{Danehkar}, Ashkbiz and {Oey}, M.~S. and {Gray}, William~J.}, title = {Catastrophic Cooling in Superwinds. II. Exploring the Parameter Space}, journal = {ApJ}, volume = {921}, number = {1}, pages = {91}, year = {2021}, doi = {10.3847/1538-4357/ac1a76} }

Learn More Website: https://superwinds.astro.lsa.umich.edu/
GitPage: https://galacticwinds.github.io/

10.5281/zenodo.5099614

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proEQUIB: IDL Library for Plasma Diagnostics and Abundance Analysis

The Journal of Open Source Software (2018)

Ashkbiz Danehkar

The emission lines emitted from gaseous nebulae carry valuable information about the physical conditions and chemical abundances of ionized gases in these objects, as well as the interstellar reddening.We determine the electron temperature, the electron density, and the ionic abundances from the dereddened fluxes of collisionally excited lines (CEL) and recombination lines (RL) identified in nebular spectra (see e.g.

Electron temperature

Doubly ionized oxygen

10.21105/joss.00899

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galacticwinds/Catastrophic_Cooling_Superwinds_III_Data: Catastrophic-Cooling-Superwinds-III-Data.1.1

Zenodo (CERN European Organization for Nuclear Research) (2022)

Ashkbiz Danehkar M. S. Oey William J. Gray

Catastrophic Cooling in Superwinds. III. Non-equilibrium Photoionization, Supplementary Material The files of the interactive figure (192 images) of Figure 3, and the compressed (tar.gz) file of the 3 machine-readable table files (a portion shown for guidance regarding its form and content in Table 1) are archived on Zenodo. Figure 3. Top Panels: The hydrogen temperature profiles (left panels) along with the adiabatic prediction (red dashed line) in the CPI and NPI cases, and the line emissivities (right panels) of the superwind models on a logarithmic scale, from top to bottom, in the CPI and NPI cases. Bottom Panels: The hydrogen density profiles (left panels) along with the adiabatic prediction (red dashed lines), and the ionic fractions (right panels) on a logarithmic scale for the CPI and NPI cases. The start and end of the hot bubble (region b), the end of the shell (region c), and the Strömgren radius are shown by dotted, dashed, dash-dotted, and solid lines (gray color), respectively. Table 1. Integrated luminosities (unit in erg/s) from the different ionization models. Citation

@article{Danehkar2021, author = {{Danehkar}, A. and {Oey}, M.~S. and {Gray}, W.~J.}, title = {Catastrophic Cooling in Superwinds. III. Nonequilibrium Photoionization}, journal = {ApJ, accepted}, volume = {937}, number = {2}, pages = {68}, year = {2022}, doi = {10.3847/1538-4357/ac8cec} }

Learn More Website: https://superwinds.astro.lsa.umich.edu/
GitPage: https://galacticwinds.github.io/

10.5281/zenodo.6601127

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Book Review: Gauge/Gravity Duality: Foundations and Applications

Frontiers in Physics (2018)

Ashkbiz Danehkar

BOOK REVIEW article Front. Phys., 31 August 2018Sec. High-Energy and Astroparticle Physics Volume 6 - 2018 | https://doi.org/10.3389/fphy.2018.00082

Duality (order theory)

Astroparticle physics

10.3389/fphy.2018.00082

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Bi-Abundance Ionisation Structure of the Wolf–Rayet Planetary Nebula PB 8

Publications of the Astronomical Society of Australia (2018)

Ashkbiz Danehkar

Abstract The planetary nebula PB 8 around a [WN/WC]-hybrid central star is one of planetary nebulae with moderate abundance discrepancy factors (ADFs ~ 2–3), which could be an indication of a tiny fraction of metal-rich inclusions embedded in the nebula (bi-abundance). In this work, we have constructed photoionisation models to reproduce the optical and infrared observations of the planetary nebula PB 8 using a non-LTE stellar model atmosphere ionising source. A chemically homogeneous model initially used cannot predict the optical recombination lines. However, a bi-abundance model provides a better fit to most of the observed optical recombination lines from N and O ions. The metal-rich inclusions in the bi-abundance model occupy 5.6% of the total volume of the nebula, and are roughly 1.7 times cooler and denser than the mean values of the surrounding nebula. The N/H and O/H abundance ratios in the metal-rich inclusions are ~1.0 and 1.7 dex larger than the diffuse warm nebula, respectively. To reproduce the Spitzer spectral energy distribution of PB 8, dust grains with a dust-to-gas ratio of 0.01 (by mass) were also included. It is found that the presence of metal-rich inclusions can explain the heavy element optical recombination lines, while a dual-dust chemistry with different grain species and discrete grain sizes likely produces the infrared continuum of this planetary nebula. This study demonstrates that the bi-abundance hypothesis, which was examined in a few planetary nebulae with large abundance discrepancies (ADFs > 10), could also be applied to those typical planetary nebulae with moderate abundance discrepancies.

Wolf–Rayet star

10.1017/pasa.2018.1

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Citations (7)

Morphokinematics and abundances analysis of Galactic planetary nebulae with binary central stars

Ashkbiz Danehkar

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Discovery of an Ultraviolet Counterpart to an Ultrafast X-Ray Outflow in the Quasar PG 1211+143

The Astrophysical Journal (2018)

G. A. Kriss Julia C. Lee Ashkbiz Danehkar Michael A. Nowak Taotao Fang

Abstract We observed the quasar PG 1211+143 using the Cosmic Origins Spectrograph on the Hubble Space Telescope in 2015 April as part of a joint campaign with the Chandra X-ray Observatory and the Jansky Very Large Array. Our ultraviolet spectra cover the wavelength range 912–2100 Å. We find a broad absorption feature ( ) at an observed wavelength of 1240 Å. Interpreting this as H i Ly α , in the rest frame of PG 1211+143 ( z = 0.0809), this corresponds to an outflow velocity of −16,980 (outflow redshift ), matching the moderate ionization X-ray absorption system detected in our Chandra observation and reported previously by Pounds et al. With a minimum H i column density of , and no absorption in other UV resonance lines, this Ly α absorber is consistent with arising in the same ultrafast outflow as the X-ray absorbing gas. The Ly α feature is weak or absent in archival ultraviolet spectra of PG 1211+143, strongly suggesting that this absorption is transient, and intrinsic to PG 1211+143. Such a simultaneous detection in two independent wavebands for the first time gives strong confirmation of the reality of an ultrafast outflow in an active galactic nucleus.

Ultraviolet

Outflow

10.3847/1538-4357/aaa42b

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Citations (14)