SWIR at the Nordic Optical Telescope: NOTCam

Abbott, T. M. C.; Aspin, C.; Sørensen, Anton Norup; Nørregaard, P.; Andersen, J.F.; Andersen, M. I.; Bliek, N. S. van der; Clasen, J. W.; Cox, Geoff; Klougart, Jens; Larsen, H. H.; Michaelsen, Niels; Noël, Benjamin; Olofsson, G.; Pérez, Carlos Mazo; Schwarz, Hugo E.

doi:10.1117/12.395528

Cited by 12 publications

(4 citation statements)

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“…Photometric observations were obtained with the NOT nearinfrared camera and spectrograph (NOTCam; Abbott et al 2000) on 25 January and 18 February 2021 (program 62-410, PI: F. Lykou), with the high-resolution (HR) imaging mode in standard J, H, and K s filters. The detector array (1024 × 1024 pixels) offers a field-of-view of 80 × 80 in HR mode with a plate scale of 0.078 /pixel.…”

Section: Nordic Optical Telescopementioning

confidence: 99%

The disk of FU Orionis viewed with MATISSE/VLTI

Lykou

Ábrahám

Chen

et al. 2022

A&A

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Aims. We studied the accretion disk of the archetypal eruptive young star FU Orionis with the use of mid-infrared interferometry, which enabled us to resolve the innermost regions of the disk down to a spatial resolution of 3 milliarcseconds (mas) in the L band, that is, within 1 au of the protostar. Methods. We used the interferometric instrument MATISSE/VLTI to obtain observations of FU Ori’s disk in the L, M, and N bands with multiple baseline configurations. We also obtained contemporaneous photometry in the optical (UBVRIr′i′; SAAO and Konkoly Observatory) and near-infrared (JHKs; NOT). Our results were compared with radiative transfer simulations modeled by RADMC-3D. Results. The disk of FU Orionis is marginally resolved with MATISSE, suggesting that the region emitting in the thermal infrared is rather compact. An upper limit of ~1.3 ± 0.1 mas (in L) can be given for the diameter of the disk region probed in the L band, corresponding to 0.5 au at the adopted Gaia EDR3 distance. This represents the hot, gaseous region of the accretion disk. The N-band data indicate that the dusty passive disk is silicate-rich. Only the innermost region of said dusty disk is found to emit strongly in the N band, and it is resolved at an angular size of ~5 mas, which translates to a diameter of about 2 au. The observations therefore place stringent constraints for the outer radius of the inner accretion disk. Dust radiative transfer simulations with RADMC-3D provide adequate fits to the spectral energy distribution from the optical to the submillimeter and to the interferometric observables when opting for an accretion rate M ~ 2 × 10−5 M⊙ yr−1 and assuming M* = 0.6 M⊙, Most importantly, the hot inner accretion disk’s outer radius can be fixed at 0.3 au. The outer radius of the dusty disk is placed at 100 au, based on constraints from scattered-light images in the literature. The dust mass contained in the disk is 2.4 × 10−4 M⊙, and for a typical gas-to-dust ratio of 100, the total mass in the disk is approximately 0.02 M⊙. We did not find any evidence for a nearby companion in the current interferometric data, and we tentatively explored the case of disk misalignment. For the latter, our modeling results suggest that the disk orientation is similar to that found in previous imaging studies by ALMA. Should there be an asymmetry in the very compact, inner accretion disk, this might be resolved at even smaller spatial scales (≤1 mas).

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Section: Nordic Optical Telescopementioning

confidence: 99%

The disk of FU Orionis viewed with MATISSE/VLTI

Lykou

Ábrahám

Chen

et al. 2022

A&A

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“…The most recent JHK S photometry is not archival, but was obtained by ourselves on 25 April 2023 with the NOTCam instrument (Abbott et al 2000) at the Nordic Optical Telescope (NOT; Djupvik & Andersen 2010). The seeing during the observation was about 0.…”

Section: Discussionmentioning

confidence: 99%

A radical transition in the post-main-sequence system U Equulei

Kamiński,

Schmidt,

Djupvik

et al. 2024

A&A

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U Equ is an unusual maser-hosting infrared source discovered in the 1990s. It was tentatively classified as a post-asymptotic giant branch (post-AGB) star with a unique optical spectrum displaying rare emission and absorption features from molecular gas at a temperature of about 500\,K. In 2022, we serendipitously discovered that its optical spectrum had drastically changed since the last observations in the 1990s. We aim to characterize the drastic change in the spectrum and analyze the photometric behavior of the object since 1989. Optical high-resolution spectra of U\,Equ from the Southern African Large Telescope were supplemented by archival data and near-infrared photometry from the Nordic Optical Telescope. New spectral line observations with the Effelsberg 100\,m radio telescope and Atacam Large Millimeter Array are presented. Radiative transfer modeling of multiple epoch spectral energy distributions was performed. No circumstellar molecular features are present in the contemporary optical spectra of U\,Equ. Nonphotospheric absorption and emission from neutral and ionized species dominate the current spectrum. Some of the observed features indicate an outflow with a projected terminal velocity of 215\ Broad H K lines of Ca II indicate a photosphere of spectral type F or similar. For the first time, we find SiO $J=$1--0 varv =1 maser emission in U\,Equ. Our collected photometric measurements show that the source has monotonically increased its optical and near-infrared fluxes since about the beginning of this century and continues to do so. The current rise in the optical regime is about 1 mag. Spectral energy distributions at different epochs show dusty circumstellar material that is very likely arranged in a highly inclined disk. Adopting a distance of 4\,kpc, informed by the Gaia parallax of U\,Equ, we find that the source luminosity is about 10$^4$ sun $. This luminosity has likely increased by a factor of a few in the last decades, which is most probably related to the drastic change in the optical circumstellar spectrum of the object. The object has changed considerably in the past three decades, either due to geometrical reconfiguration of the circumstellar medium, evolutionary changes in the central star, or owing to an accretion event that started very recently in the system. Observationally, U\,Equ appears to resemble category\,0 of disk-hosting post-AGB stars reported previously, especially the post-common-envelope binary HD\,101584. It is uncertain whether the drastic spectral change and the associated optical and mid-infrared rise in brightness witnessed in U\,Equ are common in post-AGB stars, but this radical change may be related to the real-time onset of the evolution of the system into a planetary nebula. We find that the post-AGB star V576\,Car has undergone a similar transformation as U\,Equ in the past few decades, which means that the phenomenon is not extremely rare.

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“…3.2 and 3.4. On 21 October 2012, we also obtained R = 2500 spectra with NOTCam (Abbott et al, 2000) at the Nordic Optical Telescope on the island of La Palma, Spain, covering the range ∼ 820 − 2360 nm. These observations where motivated by the fact that LX Cyg was observed by Joyce et al (1998) at low resolution in the J-band in 1994; our spectra provide for a check of the spectral changes that might have happened between 1994 and 2012.…”

Section: Observationsmentioning

confidence: 99%

LX Cygni: A carbon star is born

Uttenthaler

Meingast

Lebzelter

et al. 2016

A&A

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Context. The Mira variable LX Cygni (LX Cyg) has shown a dramatic increase of its pulsation period in the recent decades and is appearing to undergo an important transition in its evolution. Aims. We aim to investigate the spectral type evolution of this star over recent decades as well as during one pulsation cycle in more detail and discuss it in connection with the period evolution. Methods. We present optical, near-and mid-infrared low-resolution as well as optical high-resolution spectra to determine the current spectral type. The optical spectrum of LX Cyg has been followed for more than one pulsation cycle. We compare recent spectra to archival spectra to trace the spectral type evolution, and we analyse a Spitzer mid-IR spectrum for the presence of molecular and dust features. Furthermore, the current pulsation period is derived from AAVSO data. Results. We found that the spectral type of LX Cyg changed from S to C sometime between 1975 and 2008. Currently, the spectral type C is stable during a pulsation cycle. We show that spectral features typical of C-type stars are present in its spectrum from ∼0.5 to 14 μm, and attribute an emission feature at 10.7 μm to SiC grains. Within only 20 yr, the pulsation period of LX Cyg has increased from ∼460 d to ∼580 d and is stable now. Conclusions. We conclude that the change in spectral type and increase in pulsation period happened simultaneously and are causally connected. Both a recent thermal pulse and a simple surface temperature decrease appear unlikely to explain the observations. We therefore suggest that the underlying mechanism is related to a recent third dredge-up mixing event that brought up carbon from the interior of the star, i.e. that a genuine abundance change happened. We propose that LX Cyg is a rare transition type object that is uniquely suited to study the transformation from oxygen-to carbon-rich stars in detail.

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SWIR at the Nordic Optical Telescope: NOTCam

Cited by 12 publications

References 0 publications

The disk of FU Orionis viewed with MATISSE/VLTI

The disk of FU Orionis viewed with MATISSE/VLTI

A radical transition in the post-main-sequence system U Equulei

LX Cygni: A carbon star is born

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