Y Gem, a symbiotic star outshone by its asymptotic giant branch primary component

D. A. Vasquez-Torres; J. A. Toal\'a; J. B. Rodr\'iguez-Gonz\'alez; M. A. Guerrero; R. Ortiz

REVIEW 3 major objections 6 minor 25 references

Y Gem, a symbiotic star outshone by its asymptotic giant branch primary component

T0 review · 3 major / 6 minor · reviewed 2026-08-12 · deepseek-v4-flash

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Pith's one-line read Y Gem is an S-type symbiotic star whose hidden companion is an accreting white dwarf, not a main-sequence star.

desk verdict Y Gem being a symbiotic star is now on solid footing, but the abstract's Teff≈60,000 K and stable-burning claims are undercut by the paper's own extinction caveat and He ii nondetection. read the letter →

arxiv 2411.14270 v2 pith:Q33JFK44 submitted 2024-11-21 astro-ph.SR astro-ph.HE

M. A. Guerrero , D. A. Vasquez-Torres , J. B. Rodríguez-González , J. A. Toalá , R. Ortiz This is my paper · ORCID

classification astro-ph.SRastro-ph.HE PACS 97.80.Fk

keywords symbioticstarsYGemAGBwhitedwarfaccretionX-rayreflectionultravioletspectroscopymassratebinary

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

Y Gem is a bright AGB star whose own glare hides whatever orbits it, yet it has been known for decades to emit far-UV and X-rays. This paper argues that those emissions come from a white dwarf companion accreting the giant's wind, which would make Y Gem a symbiotic system rather than an AGB star with a main-sequence partner. The paper assembles the first optical spectrum, re-reduces public UV and X-ray spectra, and fits the X-ray data with reflection models to separate accretion from jets and reflection. If its interpretation holds, Y Gem's white dwarf is accreting at about $2.5\times10^{-7}\,M_\odot\,\mathrm{yr}^{-1}$ and sits in a stable, steady burning phase with no recurrent eruptions, and Y Gem becomes one of the brightest UV and X-ray symbiotic stars known.

What carries the argument

The argument is carried by a multicomponent spectral decomposition together with physically motivated X-ray reflection tables. Before any stellar decomposition, the ultraviolet spectrum is dereddened using $A_V=0.80$ mag from the observed H$\alpha$/H$\beta$ ratio, and this correction is what makes the far-UV ramp require a $\sim60{,}000$ K blackbody. The cool giant is identified by fitting synthetic stellar spectra to the optical spectrum and $G_{rp}$, $J$, $K$, $L$, $M$ photometry; the residual between the sum of the giant plus hot star and the observed continuum gives the disk luminosity $L_\mathrm{disk}=28\,L_\odot$. In X-rays, radiative-transfer reflection tables for a flared disk ($N_{\mathrm{H,ref}}=5\times10^{24}$ cm$^{-2}$, outer radius 1.25 AU, inclination $\theta=50^\circ$) are used in place of ad hoc Gaussian line fits, letting the authors separate the boundary-layer plasma (kT$_3$) from jet shock emission (kT$_1$, kT$_2$) and reflection. The mass-accretion rate follows from $L_\mathrm{acc}=G M_\mathrm{WD}\dot{M}_\mathrm{acc}/(2R_\mathrm{WD})$ with $M_\mathrm{WD}=0.8\,M_\odot$ and $R_\mathrm{WD}=0.11\,R_\odot$.

What would settle it

If a high-resolution, multi-epoch measurement of the Balmer lines or the 2175 Å extinction bump in the ultraviolet spectrum shows that the true extinction is close to $A_V\approx0.12$ mag, then the hot component's temperature drops to roughly 35,000--54,000 K, its radius and luminosity shrink, and the derived accretion rate falls by a factor of several, contradicting the paper's stable-burning picture.

Watch

Extended reading notes

Core claim

The central claim is that Y Gem is an S-type symbiotic star (the giant does not fill its Roche lobe, so accretion is from its wind): its hot component has $T_\mathrm{eff}\approx60{,}000$ K, $L=140\,L_\odot$, and $R=0.11\,R_\odot$, and is very likely an accreting white dwarf, while the cool component is a $1.1\,M_\odot$ AGB star with $T_\mathrm{eff}=3350$ K and $R=240\,R_\odot$. The optical spectrum shows the sawtooth molecular bands of the giant plus narrow forbidden and recombination lines, and the extinction-corrected far-UV ramp needs the hot white dwarf. The X-ray spectra of all six epochs are reproduced with soft shock components, a reflected component from a flared disk ($N_{\mathrm{H,ref}}=5\times10^{24}$ cm$^{-2}$, radius 1.25 AU, inclination $50^\circ$), and a heavily absorbed boundary-layer plasma; only the latter counts as accretion luminosity. Adding the disk excess $L_\mathrm{disk}=28\,L_\odot$ to the boundary-layer X-ray luminosity gives $\dot{M}_\mathrm{acc}=2.5\times10^{-7}\,M_\odot\,\mathrm{yr}^{-1}$, which theoretical models place in the stable steady-burning regime.

Load-bearing premise

The inferred hot-companion properties rest on the assumption that the measured H-alpha to H-beta emission ratio is true dust extinction rather than self-absorption of the emission lines themselves, even though the known interstellar reddening toward Y Gem is much smaller.

Editorial extensions

If this is right

If Y Gem is truly a symbiotic system, its reclassification removes a prominent case for the idea that X-ray-loud AGB stars generally harbor main-sequence accretors rather than white dwarfs.
The accreting white dwarf is inferred to be in the stable steady shell-burning regime, so Y Gem should not show nova-like recurrent eruptions; its UV and X-ray output should vary with the wind and accretion rate instead.
The estimated accretion rate matches the modified Bondi-Hoyle-Lyttleton prediction for an 8.87-year orbit, which favors that period over the 28.9 and 65.9-year candidates as the true binary period.
Y Gem becomes one of the brightest UV and X-ray symbiotic systems known, providing a local benchmark for identifying the suspected missing population of symbiotic stars among X-ray-emitting AGB stars.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

If the Balmer-line self-absorption explanation is correct, which the paper raises as a possibility, the hot component would be cooler, roughly $35{,}000$--$54{,}000$ K, and the white dwarf radius, luminosity, and accretion rate would shift by factors of several, weakening the stable-burning conclusion.
The two longest periods found in the light curve could be magnetic activity cycles of the giant rather than orbital periods; a multi-cycle X-ray and UV monitoring campaign could test this by looking for period-locked changes in accretion signatures.
A natural extension is to apply the same reflection-model decomposition to other X-ray-emitting AGB stars; systems currently classified as main-sequence accretors may fall into the low-luminosity tail of symbiotic systems once their boundary-layer and reflection components are separated.
The inferred disk inclination of $50^\circ$ predicts that outflow velocities measured in the UV are underestimated by a factor $\sim1/\sin 50^\circ$; high-resolution UV spectroscopy could check whether the observed $\sim\!-1000$ km s$^{-1}$ Ly$\alpha$ is a genuine high-velocity jet.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

The case that Y Gem is a symbiotic star with an accreting white dwarf is now solid, but the headline numbers—Teff≈60,000 K and the stable-burning accretion rate—are not supported by the authors' own analysis.

What's new and good: first optical spectrum, which shows [Ne iii], [O iii], H i, and He i emission; a SKIRT-based reflection model for the X-ray spectra; and a light-curve analysis that turns up plausible pulsation and candidate orbital periods. The combination of the 6.4 keV Fe line, X-ray variability, and optical high-ionization lines really does discriminate against the earlier main-sequence-companion interpretation. The cool component (Teff=3350 K, M=1.1 M⊙, R=240 R⊙) is derived with a straightforward SED fit and looks fine. If the paper only claimed the identification, I'd have little to argue with.

The soft spot is the extinction. AV=0.80 comes from the Hα/Hβ ratio, but the interstellar value is AV≈0.12 and the authors themselves say self-absorption of Hα (τ≈5) could mimic reddening. In Sec. 4.1 they explicitly say that if AV were lower, the hot component would be 35,000–54,000 K, and that the non-detection of He ii λ4686 caps Teff near 54,000 K. In Sec. 4.3 they call the WD properties "poorly constrained." Yet the abstract quotes 60,000 K, 140 L⊙, and 0.11 R⊙, and the accretion rate and stable-burning statement are built on those numbers. That's not a minor wording issue; it is a load-bearing inconsistency. The SySt classification survives, but the physical parameters and the burning-phase conclusion need to be reworked, either by justifying AV=0.80 or by presenting the AV-conditional range and dropping the stable-burning claim until the accretion rate has a real error budget.

Smaller concerns: M_WD=0.8 M⊙ is adopted from Yu et al. without independent measurement; the 8.87 yr period used for the BHL accretion estimate is one of three candidate periods and is not secure; and Ldisk is a residual from the SED subtraction with no quoted uncertainty. These are fixable.

My take: this is a worthwhile paper for the symbiotic/AGB community, and it deserves a serious referee. I'd send it to review, with the explicit instruction that the abstract and conclusions must match the body, the AV ambiguity has to be handled head-on, and the accretion-rate and stable-burning claims must be propagated through an error budget or retracted.

Referee Report

3 major / 6 minor

Summary. This paper presents the first optical spectrum of Y Gem (INT IDS, 3200–8290 Å), together with analyses of archival HST STIS UV spectra, Chandra and XMM-Newton X-ray observations, and AAVSO/ASAS-SN photometry. The optical spectrum shows TiO/VO/CaH molecular bands typical of a late-type AGB star plus narrow [Ne iii], [O iii], He i, and H i emission lines. The authors argue that these lines, the X-ray spectra (a hard plasma component plus an Fe 6.4 keV fluorescence/reflection component modeled with a grid of SKIRT radiative-transfer tables), and the near/mid-IR colors establish Y Gem as an S-type symbiotic star whose companion is an accreting white dwarf rather than a main-sequence star. They derive a hot component with Teff≈60,000 K, L=140 L☉, R=0.11 R☉, a cool AGB component with 3350 K, 240 R☉, and 1.1 M☉, and a mass-accretion rate of about 2.5×10^-7 M☉/yr, concluding that the WD is in a stable, steady shell-burning phase with no recurrent events expected.

Significance. If the classification holds, Y Gem becomes one of the brightest far-UV and X-ray symbiotic stars known and a concrete example of an X-ray/UV-bright AGB star that is a misidentified SySt, supporting the broader claim that part of the X-AGB population hosts accreting white dwarfs. The paper's strengths are specific: it supplies the previously missing optical spectrum, it replaces ad hoc Gaussian Fe-line fits with a physically motivated SKIRT reflection grid, and its classification rests on external observables (ionization-potential arguments, the 6.4 keV fluorescent line, the Balmer-decrement inconsistency) rather than on definitional circularity. The ARAS echelle spectrum provides independent confirmation of the key emission lines. The SySt classification itself is robust; what is insecure is the quantitative hot-component parameter set and the stable-burning inference, which are tied to one side of an extinction degeneracy that the authors themselves document.

major comments (3)

[Sec. 4.1 and Abstract] The abstract reports Teff≈60,000 K as a headline result, but Sec. 4.1 concludes that 'the effective temperature of the hot companion is thus constrained to be in the range of 35,000 K to 54,000 K,' and Sec. 4.3 states that the UV spectrum 'requires Teff to be ≥60,000 K.' These statements are mutually inconsistent: 60,000 K lies above the 54,000 K upper bound set by the He ii λ4686 nondetection, and the ≥60,000 K requirement contradicts the 35,000–54,000 K range that Sec. 4.1 itself derives under the lower-extinction alternative. Because L=140 L☉, R=0.11 R☉, and the accretion rate in Eq. (7) all build on this Teff, the manuscript should present a single self-consistent parameter set for each extinction scenario and align the abstract and conclusions with those sets.
[Sec. 3.1 and Sec. 4.1] The extinction A_V=0.80 is derived in Sec. 3.1 from the Hα/Hβ ratio, but the same section states that the interstellar reddening toward Y Gem is only A_V≈0.12 and that Balmer self-absorption with τ_Hα≈5 can fully mimic the observed ratio; Sec. 4.1 then concedes that a lower A_V would allow Teff=35,000–54,000 K. Nevertheless, A_V=0.80 is adopted without independent support to deredden the HST STIS and INT spectra (Figs. 8 and 9) and to derive the hot-component luminosity, radius, and accretion rate. Since the paper itself establishes a two-way degeneracy between extinction and line self-absorption, the hot-component quantities must be quoted with the A_V≈0.12 alternative propagated as a systematic uncertainty rather than presented only for the A_V=0.80 case.
[Sec. 4.2, Eq. (7)] The stable-burning conclusion is not robust to the uncertainties acknowledged elsewhere in the paper. The rate Ṁ_acc=2.5×10^-7 M☉/yr follows from Eq. (7) using R_WD=0.11 R☉ (derived from the A_V=0.80 SED fit) and L_acc=L_disk+L_X3, with L_X3 itself varying by a factor of three across epochs (0.05–0.15 L☉ in Table 4) and the adopted 0.12 L☉ near the top of that range. The conclusion that a 0.8 M☉ WD (mass assumed from Yu et al. 2022) burns stably depends on Ṁ_acc lying inside a narrow strip, so a factor-of-a-few shift in L_acc or R_WD moves the system into the recurrent-nova regime. The abstract's claim that 'no recurrent events are expected' should be replaced by a propagated range for Ṁ_acc or explicitly qualified as scenario-dependent.

minor comments (6)

[Abstract and Sec. 4.2] The abstract quotes Ṁ_acc=2.3×10^-7 M☉/yr while Sec. 4.2 and Sec. 5 give 2.5×10^-7 M☉/yr; the values should be reconciled and the adopted L_X3 averaging stated explicitly.
[Table 4] The identical χ²/DoF=170.66/161 is listed for the four epochs 2014.84, 2015.74, 2015.75, and 2015.81, which can mislead readers into thinking these are independent fits with coincidentally equal statistics; since those epochs were fitted jointly, the entry should be labeled as the joint statistic.
[Sec. 3.2] The periods PWD2?=28.9 yr and PWD3?=65.9 yr are described as possible resonance frequencies of PWD1?=8.87 yr, but the period ratios are approximately 3.3 and 2.3, which are not close to small integers; the resonance interpretation should be quantified or softened.
[Sec. 4.2] The derivation of L_disk=28 L☉ by 'subtracting the contributions of the hot WD companion and the late M-type star' is not reproducible from the text; the authors should specify the wavelength ranges, the adopted stellar parameters, and the subtraction procedure.
[Sec. 1] The sentence 'Despite the statement on the lack of optical forbidden line emission in the optical spectrum of Y Gem by Sahai et al. (2018), no optical spectra of this star are available' is self-contradictory as written and should be reworded to clarify which spectra existed before this work.
[Sec. 4.1] The statement that the far-UV slope 'requires a minimum temperature of ≈60,000 K' is not backed by a documented fit; the blackbody curves in Fig. 8 should be accompanied by the fitted wavelength range, normalization, and residuals or χ², particularly because this minimum motivates the headline Teff.

Circularity Check

0 steps flagged · score 2.0 of 10

No significant circularity: classification and accretion-rate estimates rest on external observables and standard physics; only minor self-citations appear and are not load-bearing.

full rationale

The paper's central claim that Y Gem is an S-type symbiotic system with an accreting WD is supported by newly presented optical emission lines ([Ne iii], [O iii], H i, He i), the 6.4 keV Fe fluorescent line in the X-ray spectra, and a physically motivated reflection model fitted to public Chandra/XMM data. The hot-component parameters (Teff ~ 60,000 K, L = 140 Lsun, R = 0.11 Rsun) are derived from the extinction-corrected UV and optical SED, not from the conclusion. The mass-accretion rate follows from the standard Shakura-Sunyaev formula L_acc = G M_WD Mdot / (2 R_WD) using these parameters, which is a physical conversion rather than a fitted prediction. The X-ray reflection model (SKIRT) is fitted to the data; its use of a flared disk does not presuppose the WD classification in a way that forces the result. Citations to Toalá et al. and Tejeda & Toalá are from the same group, but they are externally published physical models used to interpret the data, not uniqueness theorems or ansatze that smuggle in the conclusion. The paper's own caveat that A_V = 0.80 from the Balmer decrement may be mimicked by self-absorption, lowering Teff to 35,000-54,000 K, is a robustness/correctness concern, not a circularity: the extinction is an input fitted to one diagnostic, and the alternative Teff range is explicitly stated. The BHL cross-check uses the 8.87-yr period from the same light curve and the same group's model, but it is a consistency check rather than the source of the main Mdot estimate. No equation in the paper reduces by construction to its own input, and no 'prediction' is statistically forced by a fitted parameter.

Assumptions & free parameters 8 free parameters · 8 assumptions · 0 invented entities

The central claim rests on fitted stellar parameters, an adopted extinction, assumed WD mass, a standard accretion formula, and an interpretation of a light-curve period as orbital. No new particles, forces, or dimensions are introduced. The largest uncertainties come from the extinction correction and the assumptions feeding the accretion-rate estimate.

free parameters (8)

Visual extinction A_V = 0.80 mag (from Balmer decrement, E(B-V)=0.26)
Used to deredden UV/optical spectra; the paper notes interstellar extinction is only ~0.12 mag and self-absorption may mimic reddening, so this strongly affects hot component parameters.
Hot component effective temperature T_hot = 60,000 K (range 35,000-54,000 K discussed)
Blackbody fit to far-UV slope; uncertain due to extinction and He II nondetection.
Hot component luminosity and radius = L=140 Lsun, R=0.11 Rsun
Derived from blackbody fit and distance; would change substantially if T_hot is lower.
Cool component parameters = Teff=3350 K, log g=-0.29, L=6600 Lsun, R=240 Rsun, M=1.1 Msun
Best fit to optical and IR photometry with Lejeune et al. (1997) model grid; grid spacing limits accuracy.
White dwarf mass M_WD = 0.8 Msun (adopted from Yu et al. 2022)
Used in escape velocity and accretion rate; not independently measured in this paper.
Accretion disk luminosity L_disk = 28 Lsun
Residual after subtracting hot and cool stellar components; no error budget given.
Reflection disk parameters = NH_ref=5e24 cm^-2, R=1.25 AU, inclination=50 deg
Best joint X-ray fit to four epochs; not unique, no confidence contours shown.
Per-epoch X-ray plasma parameters = NH1, kT1, kT2, kT3, A1-A3, CF, Aref (Table 4)
Fitted with XSPEC for each epoch; some have large uncertainties.

assumptions (8)

domain assumption Gaia DR3 parallax distance d=644 pc is reliable despite RUWE issues
Adopted throughout; alternative estimate 580 pc is within 2 sigma. Section 1.
domain assumption Stellar atmosphere model grid (Lejeune et al. 1997) adequately represents Y Gem's cool AGB spectrum
Used to fit Teff, log g, L, and R; model grid spacing limits accuracy. Section 4.1.
domain assumption X-ray emission is described by apec plasma models and SKIRT reflection grids with solar abundances and fixed disk geometry
Central to separating boundary-layer X-rays from reflection and shock emission. Section 3.3.
standard math Case B recombination Halpha/Hbeta ratio applies to the Balmer lines
Used to derive E(B-V)=0.26; the paper acknowledges self-absorption may invalidate this. Section 3.1.
domain assumption Standard thin-disk accretion formula Lacc = G M Mdot/(2 R) with Lacc ≈ Ldisk + LX3 applies
Eq. (7) used to convert luminosity to accretion rate; factor-two and boundary-layer assumptions are unquantified. Section 4.2.
domain assumption The 8.87 yr periodicity in the visual light curve is the orbital period of the WD companion
Used for semimajor axis and BHL accretion check; could be an LSP or pulsation period. Section 3.2.
domain assumption AGB wind velocity 5 km/s and mass-loss rate 0.7-1e-6 Msun/yr apply for Y Gem
Used in the BHL estimate of Mdot; taken from typical SR star values, not measured for Y Gem. Section 4.3.
domain assumption Stable burning thresholds for a 0.8 Msun WD from Cassisi et al. (1998) and Wolf et al. (2013) apply
Basis for the no-recurrent-events conclusion. Section 4.2.

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Cite this review

Pith. "Pith review of Y Gem, a symbiotic star outshone by its asymptotic giant branch primary component." pith.science (2026). https://pith.science/paper/Q33JFK44

@misc{pith2026241114270,
  author       = {Pith},
  title        = {Pith review of: Y Gem, a symbiotic star outshone by its asymptotic giant branch primary component},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/Q33JFK44}},
  note         = {Machine review of arXiv:2411.14270}
}

abstract

A considerable number of asymptotic giant branch (AGB) stars exhibit UV excess and/or X-ray emission that indicates a binary companion. AGB stars are so bright that they easily outshine their companions. This almost prevents their identification. Y Gem has been known for some decades to be an AGB star that is bright in the far-UV and X-rays, but it is unclear whether its companion is a main-sequence star or a white dwarf (WD) in a symbiotic system (SySt). Our goal is to uncover the true nature of Y Gem, which will help us to study the possible misidentified population of SySts. Multiwavelength IR, optical, UV, and X-ray observations were analyzed to investigate the properties of the stellar components and the accretion process in Y Gem. In particular, an optical spectrum of Y Gem is presented here for the first time, while X-ray data are interpreted by means of reflection models produced by an accretion disk and material in its vicinity. The optical spectrum exhibits the typical sawtooth-shaped features of molecular absorptions in addition to narrow recombination and forbidden emission lines. The emission lines and the analysis of the extinction-corrected UV spectrum suggest a hot component with $T_\mathrm{eff}\approx$60,000 K, $L$=140 L$_{\odot}$, and $R$=0.11 R$_{\odot}$ that very likely is an accreting WD. The late component is found to be an 1.1 M$_\odot$ AGB star with $T_\mathrm{eff}$=3350 K and $R$=240 R$_\odot$. Using IR, optical, UV, and X-ray data, we found that Y Gem is an S-type SySt whose compact component is accreting at an estimated mass-accretion rate of $\dot{M}_\mathrm{acc}=2.3\times10^{-7}$ M$_\odot$ yr$^{-1}$. At this accretion rate, the accreting WD has reached the stable and steady burning phase in which no recurrent events are expected.

Figures

Figures reproduced from arXiv: 2411.14270 by the authors.

**Figure 1.** 2.2. X-ray data Y Gem was observed on several occasions with Chandra and XMM-Newton, which allows monitoring its extreme variations in the 0.3–10.0 X-ray band (e.g., Ortiz & Guerrero 2021; Sahai et al. 2011, 2015; Yu et al. 2022). The details of the observations used here are presented in [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗

**Figure 1.** (top) Flux-calibrated INT IDS optical spectrum of Y Gem and (bottom) zoomed views of the emission lines of interest. ferent epochs: 2014 March 31 (2014.25), 2015 September 29 (2015.74), 2015 October 1 (2015.75), and 2015 October 23 (2015.81). The observation data files were retrieved from the XMM-Newton Science Archive2 . We processed the EPIC data using the Science Analysis Software (SAS; Gabriel et al. 2004) versi… view at source ↗

**Figure 2.** Chandra ACIS-S and XMM-Newton EPIC-pn backgroundsubtracted medium-resolution X-ray spectra of Y Gem (see [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗

Figures from the paper (6 more)

**Figure 3.** Figure 3: Optical spectra of Y Gem and the iconic SySts R Aqr, oCet, and T CrB obtained from the ARAS spectral database of eruptive stars. The spectra are presented in relative flux, normalized to the intensity of the sawtooth-shaped spectral feature at ≈6100 Å [PITH_FULL_IMAGE…

**Figure 4.** Figure 4: Light curve in the visual band of Y Gem obtained from AAVSO. The dashed line represents the 2.5th percentile, which defines the minimum magnitude of 8.80 mag, and the dotted line corresponds to the 97.5th percentile and marks the maximum magnitude of 10.40 mag. The mag…

**Figure 5.** Figure 5: Power spectrum of the visual band light curve from AAVSO. The peaks with significant power values are classified as a signal, and the peaks below the blue line, indicating the FAP with a probability of 0.05, are classified as noise. defined by the 2.5th and 97.5th perc…

**Figure 6.** Figure 6: Period-folded light curves of Y Gem in the visual band from AAVSO plotted as a function of phase for the most promising periods derived from the LS analysis. The dashed white line in each panel represents the corresponding period. The density map in each panel has bee…

**Figure 7.** Figure 7: Background-subtracted X-ray spectra of Y Gem. The different panels show different epochs with details from their best-fit model spectra (dark solid line). The dotted, dashed, dash-dotted, and light solid lines represent the contributions from the kT1, kT2, kT3, and the…

**Figure 8.** Figure 8: UV and optical spectra of Y Gem. The figure includes far- and near-UV spectra from HST (magenta) and the optical INT IDS spectrum (blue), both corrected for extinction assuming AV = 0.8 and the extinction curve by Cardelli et al. (1989). The black curve represents the…

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