James T. Garland

American Museum of Natural History

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Michael M. Shara

American Museum of Natural History

Stefan Gromoll

Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

Kenneth M. Lanzetta

Stony Brook University

Frederick M. Walter

Stony Brook University

D. Valls‐Gabaud

Observatoire de Paris

John K. Webb

University of Cambridge

David Zurek

American Museum of Natural History

Karen L. Masters

Haverford College

J. Mikołajewska

Nicolaus Copernicus Astronomical Center

M. J. Darnley

Liverpool John Moores University

Cooperative Institutions

Association of Universities For Research In Astronomy

American Museum of Natural History

Kitt Peak National Observatory

Stony Brook University

U.S. National Science Foundation

Space Telescope Science Institute

Max Planck Society

Max Planck Institute for Astronomy

South African Radio Astronomy Observatory

Tel Aviv University

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Hydrodynamic simulations of the KT Eridani nova super-remnant

arXiv (Cornell University) (2023)

M. W. Healy-Kalesh M. J. Darnley Michael M. Shara Kenneth M. Lanzetta James T. Garland

A nova super-remnant (NSR) is an immense structure associated with a nova that forms when frequent and recurrent nova eruptions sweep up surrounding interstellar material (ISM) into a high density and distant shell. The prototypical NSR, measuring over 100 pc across, was discovered in 2014 around the annually erupting nova M31N 2008-12a. Hydrodynamical simulations demonstrated that the creation of a dynamic NSR by repeated eruptions transporting large quantities of ISM is not only feasible but that these structures should exist around all novae, whether the white dwarf (WD) is increasing or decreasing in mass. But it is only the recurrent nova (RNe) with the highest WD masses and accretion rates that should host observable NSRs. KT Eridani is, potentially, the eleventh RNe recorded in the Galaxy and is also surrounded by a recently unveiled H{\alpha} shell tens of parsecs across, consistent with a NSR. Through modelling the nova ejecta from KT Eri, we demonstrate that such an observable NSR could form in approximately 50,000 years, which fits with the proper motion history of the nova. We compute the expected H{\alpha} emission from the KT Eri NSR and predict that the structure might be accessible to wide-field X-ray facilities.

Nova (rocket)

10.48550/arxiv.2310.17258

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Introducing the Condor Array Telescope: IV. A possible nova super-remnant surrounding the putative recurrent nova KT Eridani

arXiv (Cornell University) (2023)

Michael M. Shara Kenneth M. Lanzetta James T. Garland Stefan Gromoll D. Valls‐Gabaud

Just 10 recurrent novae (RNe) - which erupt repeatedly on timescales shorter than one century - are known in our Galaxy. The most extreme RN known (located in the Andromeda galaxy), M31N 2008-12a, undergoes a nova eruption every year, and is surrounded by a vast nova "super-remnant", 134 pc in extent. Simulations predict that all RNe should be surrounded by similar vast shells, but previous searches have failed to detect them. KT Eri has recently been suggested to be a RN, and we have used the Condor Array Telescope to image its environs through multiple narrowband filters. We report the existence of a large ($\sim$ 50 pc diameter), H$\,\alpha$-bright shell centered on KT Eri, exactly as predicted. This strongly supports the claim that KT Eri is the 11th Galactic recurrent nova, and only the second nova known to be surrounded by a super-remnant. SALT spectra of the super-remnant demonstrate that its velocity width is consistent with that of M31-2008-12a.

Nova (rocket)

10.48550/arxiv.2310.17055

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H i-rich but low star formation galaxies in MaNGA: physical properties and comparison to control samples

Monthly Notices of the Royal Astronomical Society (2023)

Anubhav Sharma Karen L. Masters David V. Stark James T. Garland Niv Drory

ABSTRACT Gas-rich galaxies are typically star forming. We make use of H i-MaNGA, a programme of H i follow-up for the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey of the Sloan Digital Sky Surveys, to construct a sample of unusual neutral hydrogen (H i, 21 cm)-rich galaxies that have low star formation rates (SFRs), using infrared colour from the Wide-field Infrared Survey Explorer as a proxy for specific SFR. Out of a set of 1575 MaNGA galaxies with H i-MaNGA detections, we find that 83 (5 per cent) meet our selection criteria to be H i rich with low SFR. We construct two stellar mass-matched control samples: H i-rich galaxies with typical SFR (high SF control) and H i-poor galaxies with low SFR (low H i control). We investigate the properties of each of these samples, comparing physical parameters such as ionization state maps, stellar and ionized gas velocity and dispersion, environment measures, metallicity, and morphology to search for the reasons why these unusual H i-rich galaxies are not forming stars. We find evidence for recent external accretion of gas in some galaxies (via high counter-rotating fractions), along with some evidence for active galactic nucleus (AGN) feedback (from a high central low-ionization emission-line region and/or red geyser fraction), and bar quenching (via an enhanced strong bar fraction). Some galaxies in the sample are consistent with simply having their H i in a high angular momentum, large-radius, low-density disc. We conclude that no single physical process can explain all H i-rich, low-SFR galaxies.

Stellar mass

10.1093/mnras/stad2695

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Speckle Imaging of Gamma2 Velorum: The Inner Wind Possibly Resolved

arXiv (Cornell University) (2023)

Michael M. Shara Steve B. Howell Elise Furlan James T. Garland A. F. J. Moffat

Accurately quantifying the rates dM/dt at which massive stars lose mass is essential to any understanding of their evolution. All dM/dt estimates to date assume wind clumping factors; not allowing for clumping leads to overestimates of dM/dt and underestimates of lifetimes and masses when these stars explode as supernovae. Mid-IR spectroscopy suggested that the wind of the nearest Wolf-Rayet star, Gamma2 Vel, is resolved with a Full Width at 10 per cent intensity of 0.5 arcsec, or 171 AU at the 342 pc distance of the star. As the Zorro speckle imager on Gemini-South is capable of 0.02 arcsec resolution, we have used it to image Gamma2 Vel at two orbital phases (0.30 and 0.44) with two narrowband and two intermediate-band filters in an attempt to resolve its wind. Our observations demonstrate that the wind of Gamma2 Vel may be resolved as a 0.07 arcsec westward elongation through an 832 nm filter at orbital phase 0.3 . If confirmed, this is the smallest scale (24 AU) at which a WR star wind asymmetry has been directly imaged. Similar imaging at multiple phases is needed to determine if the asymmetry is due to stochastic wind clumping, co-rotating interaction regions or colliding-wind, cone-shaped shocks.

Wolf–Rayet star

Speckle imaging

10.48550/arxiv.2308.07443

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Introducing the Condor Array Telescope: III. The expansion and age of the shell of the dwarf nova Z Camelopardalis, and detection of a second, larger shell

Michael M. Shara Kenneth M. Lanzetta James T. Garland Stefan Gromoll D. Valls‐Gabaud

Nova (rocket)

Dwarf nova

10.48550/arxiv.2310.00123

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Citations (1)

Hydrodynamic simulations of the KT Eridani nova super-remnant

Monthly Notices of the Royal Astronomical Society (2023)

M W Healy-Kalesh M. J. Darnley Michael M. Shara Kenneth M. Lanzetta James T. Garland

ABSTRACT A nova super-remnant (NSR) is an immense structure associated with a nova that forms when frequent and recurrent nova (RN) eruptions sweep up surrounding interstellar medium (ISM) into a high-density and distant shell. The prototypical NSR, measuring over 100 pc across, was discovered in 2014 around the annually erupting nova M 31N 2008-12a. Hydrodynamical simulations demonstrated that the creation of a dynamic NSR by repeated eruptions transporting large quantities of ISM is not only feasible but that these structures should exist around all novae, whether the white dwarf (WD) is increasing or decreasing in mass. But it is only the RN with the highest WD masses and accretion rates that should host observable NSRs. KT Eridani is, potentially, the eleventh RNe recorded in the Galaxy and is also surrounded by a recently unveiled H α shell tens of parsecs across, consistent with an NSR. Through modelling the nova ejecta from KT Eri, we demonstrate that such an observable NSR could form in approximately 50 000 yr, which fits with the proper motion history of the nova. We compute the expected H α emission from the KT Eri NSR and predict that the structure might be accessible to wide-field X-ray facilities.

Nova (rocket)

Dwarf nova

10.1093/mnras/stad3190

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The Newly Discovered Nova Super-remnant Surrounding Recurrent Nova T Coronae Borealis: Will it Light Up during the Coming Eruption?

The Astrophysical Journal Letters (2024)

Michael M. Shara Kenneth M. Lanzetta Alexandra Masegian James T. Garland Stefan Gromoll

Abstract A century or less separates the thermonuclear-powered eruptions of recurrent novae (RNe) in the hydrogen-rich envelopes of massive white dwarfs. The colliding ejecta of successive RN events are predicted to always generate very large (tens of parsecs) super-remnants; only two examples are currently known. T CrB offers an excellent opportunity to test this prediction. As it will almost certainly undergo its next, once in ∼80 yr RN event between 2024 and 2026, we carried out very deep narrowband and continuum imaging to search for the predicted, piled-up ejecta of the past millennia. While nothing is detected in continuum or narrowband [O iii ] images, a ∼30 pc diameter, faint nebulosity surrounding T CrB is clearly present in deep H α , [N ii ], and [S ii ] narrowband Condor Array Telescope imagery. We predict that these newly detected nebulosities, as well as the recent ejecta that have not yet reached the super-remnant, are far too optically thin to capture all but a tiny fraction of the photons emitted by RN flashes. We thus predict that fluorescent light echoes will not be detectable following the imminent nova flash of T CrB. Dust may be released by the T CrB red giant wind in preeruption outbursts, but we have no reliable estimates of its quantity or geometrical distribution. While we cannot predict the morphology or intensity of dust-induced continuum light echoes following the coming flash, we encourage multiepoch Hubble Space Telescope optical imaging as well as James Webb Space Telescope infrared imaging of T CrB during the year after it erupts.

Nova (rocket)

10.3847/2041-8213/ad991e

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Discovery of a 25 parsec-long precessing jet emanating from the old nova GK Persei

arXiv (Cornell University) (2024)

Michael M. Shara Kenneth M. Lanzetta James T. Garland D. Valls‐Gabaud Stefan Gromoll

Classical nova eruptions result from thermonuclear-powered runaways in, and ejection of, the hydrogen-rich envelopes of white dwarf stars accreted from their close binary companions. Novae brighten to up to 1,000,000 solar luminosities, and recur thousands of times over their lifetimes spanning several billion years. Between eruptions, mass transfer from the donor star to the white dwarf proceeds via an accretion disk unless the white dwarf possesses a strong magnetic field which can partially or totally disrupt the disk. In that case, accretion is focussed by the white dwarf's magnetic field towards its magnetic poles. Optical spectroscopy and interferometric radio maps demonstrate the presence of bipolar jets, typically arcsec in angular size, and orders of magnitude smaller than one parsec in linear size, during the days to months after nova eruptions. These jets expel collimated matter from the white dwarfs in nova binary stars, but well-resolved images of them are lacking. Here we report the Condor telescope's detection of a hitherto unknown, highly resolved and braided jet, three degrees (at least 25 parsecs) in length. The jet originates at the white dwarf of the old nova GK Persei (nova Per 1901 CE). It precesses on a ~ 3600 yr timescale, and must be at least 7200 years old. Detected across four decades of wavelength, the jet's ultimate energy source is likely the strong accretion shocks near the white dwarf's magnetic poles.

Intermediate polar

Black dwarf

Nova (rocket)

10.48550/arxiv.2410.12103

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Speckle imaging of γ2 Velorum: the inner wind possibly resolved

Monthly Notices of the Royal Astronomical Society (2023)

Michael M. Shara Steve B. Howell Elise Furlan James T. Garland A. F. J. Moffat

ABSTRACT Accurately quantifying the rates dM/dt at which massive stars lose mass is essential to any understanding of their evolution. All dM/dt estimates to date assume wind clumping factors; not allowing for clumping leads to overestimates of dM/dt and underestimates of lifetimes and masses when these stars explode as supernovae. Mid-infrared spectroscopy suggested that the wind of the nearest Wolf–Rayet (WR) star, γ2 Vel, is resolved with a full width at 10 per cent intensity of 0.5 arcsec, or 171 au at the 342 pc distance of the star. As the Zorro speckle imager on Gemini South is capable of ∼0.02 arcsec resolution, we have used it to image γ2 Vel at two orbital phases (0.30 and 0.44) with two narrow-band and two intermediate-band filters in an attempt to resolve its wind. Our observations demonstrate that γ2 Vel’s wind may be resolved as a ∼0.07 arcsec westward elongation through an 832 nm filter at orbital phase 0.3. If confirmed, this is the smallest scale (∼24 au) at which a WR star wind asymmetry has been directly imaged. Similar imaging at multiple phases is needed to determine if the asymmetry is due to stochastic wind clumping, co-rotating interaction regions or colliding-wind, cone-shaped shocks.

Wolf–Rayet star

Speckle imaging

10.1093/mnras/stad2482

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Citations (1)

Introducing the Condor Array Telescope – III. The expansion and age of the shell of the dwarf nova Z Camelopardalis, and detection of a second, larger shell

Monthly Notices of the Royal Astronomical Society (2024)

Michael M. Shara Kenneth M. Lanzetta James T. Garland Stefan Gromoll D. Valls‐Gabaud

ABSTRACT The existence of a vast nova shell surrounding the prototypical dwarf nova Z Camelopardalis (Z Cam) proves that some old novae undergo metamorphosis to appear as dwarf novae thousands of years after a nova eruption. The expansion rates of ancient nova shells offer a way to constrain both the time between nova eruptions and the time for post-nova mass transfer rates to decrease significantly, simultaneously testing nova thermonuclear runaway models and hibernation theory. Previous limits on the expansion rate of part of the Z Cam shell constrain the inter-eruption time between Z Cam nova events to be >1300 yr. Deeper narrow-band imaging of the ejecta of Z Cam with the Condor Array Telescope now reveals very low surface brightness areas of the remainder of the shell. A second, even fainter shell is also detected, concentric with and nearly three times the size of the ‘inner’ shell. This is the first observational support of the prediction that concentric shells must surround the frequently erupting novae of relatively massive white dwarfs. The Condor images extend our Z Cam imaging baseline to 15 yr, yielding the inner shell’s expansion rate as v = 83 ± 37 km s−1 at 23 deg south of west, in excellent agreement with our 2012 prediction. This velocity corresponds to an approximate age of $t = 2672^{-817}_{+2102}$ yr. While consistent with the suggestion that the most recent nova eruption of Z Cam was the transient recorded by Chinese imperial astrologers in the year 77 bce, the age uncertainty is still too large to support or disprove a connection with Z Cam.

Nova (rocket)

10.1093/mnras/stad3220

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Citations (2)