J/A+A/682/A133 U Equ spectra and multi-photometry (Kaminski+, 2024)
A radical transition in the post-main-sequence system U Equulei.
Kaminski T., Schmidt R.M., Djupvik A.A., Menten K.M., Kraus A.,
Itkiewicz K., Steinmetz T., Zain Mobeen M., Szczerba R.
<Astron. Astrophys. 682, A133 (2024)>
=2024A&A...682A.133K 2024A&A...682A.133K (SIMBAD/NED BibCode)
ADC_Keywords: Radio lines ; Spectroscopy ; Stars, peculiar ; Stars, masers ;
Stars, halo
Keywords: stars: AGB and post-AGB - circumstellar matter -
stars: individual: U Equ - stars: mass-loss - stars: peculiar
Abstract:
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 500K. 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 100m 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 215km/s. Broad H&K lines of [CaII] indicate a
photosphere of spectral type F or similar. For the first time, we find
SiO J=1-0 v=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 1mag. Spectral energy distributions at different epochs show
dusty circumstellar material that is very likely arranged in a highly
inclined disk. Adopting a distance of 4kpc, informed by the Gaia
parallax of U Equ, we find that the source luminosity is about
104L☉. 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.
Description:
Compilation of photometric data for U Equ (paper Figure 3) acquired
from public catalogs and our observations with the Nordic Optical
Telescope. A digital format of the Effelsberg spectra of the SiO and
water masers are included. A collection of normalized optical spectra
acquired with SALT telescope are presented for individual epochs and
after averging the spectra over time.
Objects:
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RA (2000) DE Designation(s)
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20 57 16.28 +02 58 44.54 U Equ = TIC 396436869
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
fig2sio.dat 30 2074 Effelsberg spectrum of the SiO J=1-0 v=1 line
fig2h2o1.dat 30 16202 Effelsberg spectrum of the 22 GHz maser
from Nov. 2022
fig2h2o2.dat 30 16202 Effelsberg spectrum of the 22 GHz maser
from Aug. 2023
fig3.dat 48 4064 Compilation of photometric data
list.dat 128 17 List of fits spectra
fits/* . 17 Individual fits spectra
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Byte-by-byte Description of file: fig2sio.dat fig2h2o1.dat fig2h2o2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 F16.11 km/s Vlsr LSR velocity
20- 30 E11.7 K TA Antenna temperature
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 F13.7 d MJD Modified Julian date
15- 27 E13.9 mag mag Magnitude in Band
29- 48 A20 --- Band Band (1)
--------------------------------------------------------------------------------
Note (1): Information on magnitudes:
-----------------------------------------------------
Band Number of measurements
-----------------------------------------------------
ASASSN-V 1101
ASASSN-g 2383
IOMC-V 118
Catalina-V 201
PanSTARRS-g 11
PanSTARRS-r 11
PanSTARRS-i 30
PanSTARRS-z 14
PanSTARRS-y 11
WISE-W3 12
WISE-W1 27
WISE-W2 27
WISE-W4 12
NEO-W1 18
NEO-W2 17
Arecibo-J 13
Arecibo-H 11
Arecibo-K 8
APASS-B 5
APASS-V 5
APASS-r 5
APASS-i 5
2mass-J 1
2mass-H 1
2mass-K 1
BOM96-J 1
BOM96-Ks 1
ESO-J 1
ESO-H 1
ESO-K 1
ESO-L 1
ESO-M 1
F814W 1
NOT-J 1
NOT-H 1
NOT-K 1
POSS-PanSTARRS-g-I 1
POSS-PanSTARRS-g-red 1
VISIR-NePanSTARRS-g 1
VISIR-PAH1 1
VISIR-SiC 1
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 11 F5.2 s RAs Right ascension (J2000)
12 A1 --- DE- Declination sign (J2000)
13- 14 I2 deg DEd Declination (J2000)
16- 17 I2 arcmin DEm Declination (J2000)
19- 23 F5.2 arcsec DEs Declination (J2000)
25- 30 I6 --- Nx Number of pixels along X-axis
32- 41 A10 "date" Obs.date Observation date
43- 49 F7.2 0.1nm blambda Lower value of wavelength interval
51- 57 F7.2 0.1nm Blambda Upper value of wavelength interval
59- 67 F9.7 0.1nm dlambda Wavelenght resolution
69- 71 I3 Kibyte size Size of FITS file
73- 88 A16 --- FileName Name of FITS file, in subdirectory fits
90-128 A39 --- Title Title of the FITS file
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Acknowledgements:
Tomasz Kaminski, tomkam(at)ncac.torun.pl
(End) Patricia Vannier [CDS] 14-Dec-2023