arXiv subjects

Foteini Lykou

Publications and source records attributed to Foteini Lykou.

14 recordsLinked to original sources

arXiv2026

The FU Ori outburst of PR Ori B

We report the discovery of a nearby FU Ori-type outburst (FUor), PR Ori B, in the L1641 cluster of the Orion star-forming region. The high-amplitude variability was first identified in the NEOWISE (3-5 $\mu$m) photometry of the unresolved PR Ori binary system. Long-term, resolved optical photometric monitoring demonstrates that PR Ori B is the driver of a $\Delta G=5~$mag outburst, while PR Ori A has remained constant over the last 20 years. The near-IR spectrum of PR Ori B changes from a late K-type spectral type during quiescence to a viscously heated disk during outburst, including deep absorption in $^{12}$CO and H$_2$O bands. The optical spectrum also exhibits features that are commonly associated with FUors, including P Cygni profiles in Na I D lines and absorption in the Ca II infrared triplet. The luminosity of the outburst (L$_{acc}\sim$30--40 L$_\odot$) is similar to that commonly observed in FUors. The comparison of Spitzer/IRS and VLT/VISIR spectroscopy shows some evidence of silicate crystallisation during the outburst. PR Ori B is one of the closest and brightest FUors discovered over the last few years, only one magnitude fainter than the archetype of the class FU Ori. The proximity and brightness will allow for future high angular resolution observations to probe the physics of the inner disk and to evaluate changes in the disk due to the increased luminosity.

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arXiv2026

Gaia20dsk: A new MNor discovered by the GLORIOUS collaboration

Context. Among known young stellar objects (YSOs), those exhibiting the most dramatic increases in brightness due to sudden increase in mass accretion rate are eruptive young stars. Gaia20dsk is one of the Gaia-alerted young star candidates that has displayed a double, nonperiodic brightening resembling that of other young eruptive stars. Aims. The goal of this work is to determine the physical and accretion properties of Gaia20dsk to confirm its classification as an eruptive young star. Methods. We combined publicly available optical and near-infrared (NIR) photometry with our X-shooter optical/NIR spectrum. In our analysis, we examined the optical and IR light curves from the bursts, reviewing the color-magnitude diagrams across different bands, reporting the detection of emission lines, and providing estimates of the star's accretion rates during the burst. Results. The optical light curve shows two major and one brief brightening events with a maximum amplitude of ~1.8 mag in the last five years. A classification based on spectral index indicates that Gaia20dsk is a flat-spectrum star. The X-shooter spectrum exhibit emission lines characteristic of accreting low-to-intermediate-mass young stars, displaying features typical of MNor-type objects. The mass accretion rate is between (0.5-1.8)*10^{-6} M_sun/yr. Conclusions. Gaia20dsk is an eruptive YSO that exhibits photometric features similar to those of MNors, including its characteristic brightening amplitude and burst duration, along with similar spectroscopic features and accretion rates.

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arXiv2025

Bridging stellar evolution and planet formation: from birth, to survivors of the fittest, to the second generation of planets

Stars and planets form, live, and evolve in unison. Throughout the life of a star, dusty circumstellar discs and stellar outflows influence the further evolution of both the star(s) and their orbiting planet(s). Planet-forming discs, winds of red giant branch (RGB) or asymptotic giant branch (AGB) stars, and post-RGB/post-AGB discs are examples of such host environments where dust physics plays a key role. The physical processes that occur during each of these stages establishes how the Solar System as well as exoplanetary systems were formed, are evolving, and will eventually die. This White Paper aims to bridge the fields of stellar evolution and planet formation by peering into the dust kinematics and macrostructure formation, and its effect on planet-host interaction, in dusty environments from stellar birth to death. Near-future advancements in the 2030s will enable the detection, orbital monitoring and atmospheric/mineralogical characterisation of close-in (proto)planets across diverse stages of stellar evolution. To take full advantage of these developments by the 2040s, we should develop the capabilities required to image the varied dusty environments in which planets are entrained over their lifetime. This will enable extensive testing of current theoretical understandings - from the micro-scales of dust assembly to the deeply interlinked macro-scales of planet-host interactions - across diverse settings often too small, distant, and faint to be resolved in the next decade, simultaneously providing valuable constraints on the two-way interplay of dusty host environments and planetary formation/evolution.

astro-ph.IM↗

arXiv2025

Evidence for an accretion bridge in the DX Cha circumbinary system from VLTI/MATISSE observations

DX Cha (HD 104237) is a spectroscopic binary consisting of a Herbig A7.5Ve-A8Ve primary star and a K3-type companion. Here we report on new $3.55$ micrometer interferometric observations of this source with the Multi Aperture Mid-Infrared Spectroscopic Experiment (MATISSE) at the Very Large Telescope Interferometer (VLTI). To model the four MATISSE observations obtained between 2020 and 2023, we constructed a time-dependent interferometric model of the system, using the oimodeler software. The model consists of an asymmetric ring and two point sources on a Keplerian orbit. Our best-fit model consists of a circumbinary ring with a diameter of $0.86$ au ($8.1$ mas), featuring a strong azimuthal asymmetry. We found that the position angle of the asymmetry changes tens of degrees between the MATISSE epochs. The ring is relatively narrow, with a full width at half maximum (FWHM) of $\sim$$0.13$ au ($1.23$ mas). The presence of circumstellar dust emission so close to the binary is unexpected, as previous hydrodynamic simulations predicted an inner disk cavity with a diameter of $\sim$$4$ au ($\sim$$37.5$ mas). Thus, we argue that the narrow envelope of material we detected is probably not a gravitationally stable circumbinary ring, but may be part of tidal accretion streamers channeling material from the inner edge of the disk toward the stars.

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arXiv2023

From an amateur PN candidate to the Rosetta Stone of SN Iax research

On August 25th 2013 Dana Patchick from the "Deep Sky Hunters" (DSH) amateur astronomer group discovered a diffuse nebulosity in the Wide-field Infrared Survey Explorer (WISE) mid-IR image archive that had no optical counterpart but appeared similar to many Planetary Nebulae (PNe) in WISE. As his 30th discovery he named it Pa 30 and it was added to the HASH PN database as a new PN candidate. Little did he know how important his discovery would become. 10 years later this object is the only known bound remnant of a violent double WD merger accompanied by a rare Type Iax SN, observed and recorded by the ancient Chinese and Japanese in 1181 AD. This makes Pa 30 and its central star IRAS 00500+6713 (WD J005311) the only SN Iax remnant in our Galaxy, the only known bound remnant of any SN, and based on the central star's spectrum the only Wolf-Rayet star known that neither has a massive progenitor nor is the central star of a Planetary Nebula. We cover this story and our key role in it.

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arXiv2023

A new study on a type Iax stellar remnant and its probable association with SN 1181

We report observations and modeling of the stellar remnant and presumed double-degenerate merger of Type~Iax supernova Pa30, which is the probable remnant of SN~1181~AD. It is the only known bound stellar SN remnant and the only star with Wolf-Rayet features that is neither a planetary nebula central star nor a massive Pop I progenitor. We model the unique emission-line spectrum with broad, strong O~{\sc vi} and O~{\sc viii} lines as a fast stellar wind and shocked, hot gas. Non-LTE wind modeling indicates a mass-loss rate of $\sim 10^{-6}\,\rm M_\odot\,yr^{-1}$ and a terminal velocity of $ \sim$15,000~km\,s$^{-1}$, consistent with earlier results. O~{\sc viii} lines indicate shocked gas temperatures of $T \simeq 4\,$MK. We derive a magnetic field upper limit of $B<2.5\,$MG, below earlier suggestions. The luminosity indicates a remnant mass of 1.0--1.65\,\rm M$_\odot$ with ejecta mass $0.15\pm0.05\,\rm M_\odot$. Archival photometry suggests the stellar remnant has dimmed by $\sim$0.5 magnitudes over 100 years. A low Ne/O$\,<0.15$ argues against a O-Ne white dwarf in the merger. A cold dust shell is only the second detection of dust in a SN Iax and the first of cold dust. Our ejecta mass and kinetic energy estimates of the remnant are consistent with Type Iax extragalactic sources.

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arXiv2023

The messy death of a multiple star system and the resulting planetary nebula as observed by JWST

Planetary nebulae (PNe), the ejected envelopes of red giant stars, provide us with a history of the last, mass-losing phases of 90 percent of stars initially more massive than the Sun. Here, we analyse James Webb Space Telescope (JWST) Early Release Observation (ERO) images of the PN NGC3132. A structured, extended H2 halo surrounding an ionised central bubble is imprinted with spiral structures, likely shaped by a low-mass companion orbiting the central star at 40-60 AU. The images also reveal a mid-IR excess at the central star interpreted as a dusty disk, indicative of an interaction with another, closer companion. Including the previously known, A-type visual companion, the progenitor of the NGC3132 PN must have been at least a stellar quartet. The JWST images allow us to generate a model of the illumination, ionisation and hydrodynamics of the molecular halo, demonstrating the power of JWST to investigate complex stellar outflows. Further, new measurements of the A-type visual companion allow us to derive the value for the mass of the progenitor of a central star to date with excellent precision: 2.86+/-0.06 Mo. These results serve as path finders for future JWST observations of PNe providing unique insight into fundamental astrophysical processes including colliding winds, and binary star interactions, with implications for supernovae and gravitational wave systems.

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arXiv2021

The remnant and origin of the historical supernova 1181AD

The guest star of AD 1181 is the only historical supernova of the last millennium that is without a definite counterpart. The previously proposed association with supernova remnant 3C58 is in strong doubt because of the inferred age of this remnant. Here we report a new identification of SN 1181 with our codiscovery of the hottest known Wolf Rayet star of the Oxygen sequence (dubbed Parkers star) and its surrounding nebula Pa 30. Our spectroscopy of the nebula shows a fast shock with extreme velocities of approx. 1,100kms. The derived expansion age of the nebula implies an explosive event approx 1,000 years ago which agrees with the 1181 AD event. The on sky location also fits the historical Chinese and Japanese reports of SN 1181 to 3.5degrees. Pa 30 and Parkers star have previously been proposed to be the result of a double-degenerate merger, leading to a rare Type Iax supernova. The likely historical magnitude and the distance suggest the event was subluminous for normal supernova. This agrees with the proposed Type Iax association which would also be the first of its kind in the Galaxy. Taken together, the age, location, event magnitude and duration elevate Pa 30 to prime position as the counterpart of SN 1181. This source is the only Type Iax supernova where detailed studies of the remnant star and nebula are possible. It provides strong observational support for the double degenerate merger scenario for Type Iax supernovae.

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arXiv2020

The infrared view of dust and molecules around V4334 Sgr (Sakurai's Object): a 20-year retrospective

We present an analysis of the evolution of circumstellar dust and molecules in the environment of the very late thermal pulse object V4334 Sgr (Sakurai's Object) over a $\sim20$-year period, drawing on ground-, airborne- and space-based infrared photometry and spectroscopy. The dust emission, which started in 1997, resembles a blackbody that cooled from $\sim1200$K in 1998 August to $\sim180$K in 2016 July. The dust mass, assuming amorphous carbon, was $\sim5\times10^{-10}$M$_\odot$ in 1998 August, and we estimate that the total dust mass was $\sim2\times10^{-5}$M$_\odot$ by $\sim2016$. The appearance of a near infrared excess in 2008 suggests a new episode of (or renewed) mass loss began then. We infer lower limits on the bolometric luminosity of the embedded star from that of the dust shell, which rose to $\sim16000$L$_\odot$ before declining to $\sim3000$L$_\odot$. There is evidence for weak 6-7$μ$m absorption, which we attribute to hydrogenated amorphous carbon formed in material ejected by Sakurai's Object during a mass ejection phase that preceded the 1997 event. We detect small hydrocarbon and other molecules in the spectra, and trace the column densities in hydrogen cyanide (HCN) and acetylene (C$_2$H$_2$). We use the former to determine the $^{12}$C/$^{13}$C ratio to be $6.4\pm0.7$, 14 times smaller than the Solar System value.

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arXiv2018

Central Stars of Planetary Nebulae in Galactic Open Clusters: Providing additional data for the White Dwarf Initial-to-Final-Mass Relation

Accurate (<10%) distances of Galactic star clusters allow precise estimation of the physical parameters of any physically associated Planetary Nebula (PN) and also that of its central star (CSPN) and its progenitor. The progenitor's mass can be related to the PN's chemical characteristics and furthermore, provides additional data for the widely used white dwarf (WD) initial-to-final mass relation (IFMR) that is crucial for tracing the development of both carbon and nitrogen in entire galaxies. To date there is only one PN (PHR1315- 6555) confirmed to be physically associated with a Galactic open cluster (ESO 96 -SC04) that has a turn-off mass $\sim$2 M$_{\odot}$. Our deep HST photometry was used for the search of the CSPN of this currently unique PN. In this work, we present our results.

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arXiv2018

The curious case of II Lup: a complex morphology revealed with SAM/NACO and ALMA

We present the first-ever images of the circumstellar environment of the carbon-rich AGB star II Lup in the infrared and sub-mm wavelengths, and the discovery of the envelope's non-spherical morphology with the use of high-angular resolution imaging techniques with the sparse aperture masking mode on NACO/VLT (that enables diffraction limited resolution from a single telescope) and with ALMA. We have successfully recovered images in $Ks$ (2.18$μ$m), $L'$ (3.80$μ$m) and $M'$ (4.78$μ$m), that revealed the non-spherical morphology of the circumstellar envelope around II Lup. The stellar surface of the AGB star is unresolved (i.e. $\leq30$ mas in $Ks$) however the detected structure extends up to 110 mas from the star in all filters. Clumps have been found in the $Ks$ maps, while at lower emission levels a hook-like structure appears to extend counter-clockwise from the south. At larger spatial scales, the circumstellar envelope extends up to approximately 23 arcsec, while its shape suggests a spiral at four different molecules, namely CO, SiO, CS and HC$_3$N, with an average arm spacing of 1.7 arcsec which would imply an orbital period of 128 years for a distance of 590pc.

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arXiv2012

A close halo of large transparent grains around extreme red giant stars

Intermediate-mass stars end their lives by ejecting the bulk of their envelope via a slow dense wind back into the interstellar medium, to form the next generation of stars and planets. Stellar pulsations are thought to elevate gas to an altitude cool enough for the condensation of dust, which is then accelerated by radiation pressure from starlight, entraining the gas and driving the wind. However accounting for the mass loss has been a problem due to the difficulty in observing tenuous gas and dust tens of milliarcseconds from the star, and there is accordingly no consensus on the way sufficient momentum is transferred from the starlight to the outflow. Here, we present spatially-resolved, multi-wavelength observations of circumstellar dust shells of three stars on the asymptotic giant branch of the HR diagram. When imaged in scattered light, dust shells were found at remarkably small radii (<~ 2 stellar radii) and with unexpectedly large grains (~300 nm radius). This proximity to the photosphere argues for dust species that are transparent to starlight and therefore resistant to sublimation by the intense radiation field. While transparency usually implies insufficient radiative pressure to drive a wind, the radiation field can accelerate these large grains via photon scattering rather than absorption - a plausible mass-loss mechanism for lower-amplitude pulsating stars.

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arXiv2010

A disk inside the bipolar planetary nebula M2-9

Bipolarity in proto-planetary and planetary nebulae is associated with events occurring in or around their cores. Past infrared observations have revealed the presence of dusty structures around the cores, many in the form of disks. Characterising those dusty disks provides invaluable constraints on the physical processes that govern the final mass expulsion of intermediate-mass stars. We focus this study on the famous M2-9 bipolar nebula, where the moving lighthouse beam pattern indicates the presence of a wide binary. The compact and dense dusty core in the center of the nebula can be studied by means of optical interferometry. M2-9 was observed with VLTI/MIDI at 39-47 m baselines with the UT2-UT3 and UT3-UT4 baseline configurations. These observations are interpreted using a dust radiative transfer Monte Carlo code. A disk-like structure is detected perpendicular to the lobes and a good fit is found with a stratified disk model composed of amorphous silicates. The disk is compact, 25$\times$35 mas at 8$\rm μm$, and 37$\times$46 mas at 13$\rm μm$. For the adopted distance of 1.2 kpc, the inner rim of the disk is $\sim$15 AU. The mass represents a few percent of the mass found in the lobes. The compactness of the disk puts strong constraints on the binary content of the system, given an estimated orbital period 90-120yr. We derive masses of the binary components between 0.6--1.0M$_{\sun}$ for a white dwarf and 0.6--1.4M$_{\sun}$ for an evolved star. We present different scenarios on the geometric structure of the disk accounting for the interactions of the binary system, which includes an accretion disk as well.

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arXiv2007

A silicate disk in the heart of the Ant

We aim at getting high spatial resolution information on the dusty core of bipolar planetary nebulae to directly constrain the shaping process. Methods: We present observations of the dusty core of the extreme bipolar planetary nebula Menzel 3 (Mz 3, Hen 2-154, the Ant) taken with the mid-infrared interferometer MIDI/VLTI and the adaptive optics NACO/VLT. The core of Mz 3 is clearly resolved with MIDI in the interferometric mode, whereas it is unresolved from the Ks to the N bands with single dish 8.2 m observations on a scale ranging from 60 to 250 mas. A striking dependence of the dust core size with the PA angle of the baselines is observed, that is highly suggestive of an edge-on disk whose major axis is perpendicular to the axis of the bipolar lobes. The MIDI spectrum and the visibilities of Mz 3 exhibit a clear signature of amorphous silicate, in contrast to the signatures of crystalline silicates detected in binary post-AGB systems, suggesting that the disk might be relatively young. We used radiative-transfer Monte Carlo simulations of a passive disk to constrain its geometrical and physical parameters. Its inclination (74 degrees $\pm$ 3 degrees) and position angle (5 degrees $\pm$ 5 degrees) are in accordance with the values derived from the study of the lobes. The inner radius is 9$\pm$ 1 AU and the disk is relatively flat. The dust mass stored in the disk, estimated as 1 x 10-5Msun, represents only a small fraction of the dust mass found in the lobes and might be a kind of relic of an essentially polar ejection process.

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