arXiv subjects

Sung-Chul Yoon

Publications and source records attributed to Sung-Chul Yoon.

At least 19 recordsLinked to original sources

arXiv2026

Near-Infrared and Optical Observations of SN 2024rbc: The First Early Detection of CO and Dust in a Type Ib Supernova

We present optical and near-infrared (NIR) observations of the Type Ib supernova (SN) 2024rbc. Emission from the first CO overtone, resting on a dust continuum at $2.3-2.4$ $μ$m, was observed at 62 days post-explosion. The CO band heads are not resolved, and the emission appears broad, lacking sharp spectral features. This is the first observation of CO in the ejecta of a Type Ib SN reported in literature. The spectra of SN 2024rbc exhibit strong He I lines and numerous neutral and ionized metal lines. Comparing the spectral evolution of SN 2024rbc to other Type Ib, Ic, and IIb SNe indicates it is a Type Ib SN. We compare the velocities of key optical lines to examine the evolution of the ejecta. Additionally, fitting SN light curve models of helium star progenitors computed with the STELLA code to photometric observations indicates a $^{56}$Ni mass of $0.07$ $M_\odot$ and an ejecta mass of $1.7$ $M_\odot$. Fitting a LTE model to the CO overtone implies a CO mass of 5.2 $\times$ 10$^{-4}$ $M_{\odot}$, a CO temperature of $4040$ K, and a CO velocity width of $5905$ km s$^{-1}$. We also fitted a modified blackbody model to the dust continuum, deriving a dust temperature of $910$ K and a dust mass of $1.3$ $\times$ $10^{-3}$ $M_{\odot}$. The CO provides direct evidence for the onset of dust formation, and the observed dust continuum likely originates from newly formed dust in the ejecta. However, robust dust mass estimates require MIR observations.

astro-ph.HE↗

arXiv2026

Type Ib supernovae are bluer than Type Ic supernovae

Type Ib and Ic supernovae (SNe Ib/Ic) are the bright finale of massive stars that have lost their hydrogen envelopes, making them powerful probes of mass stripping in massive star evolution. The advent of modern large photometric and spectroscopic surveys presents a unique opportunity to investigate systematic differences between these two kinds of SNe. In this study, we analyze a large, homogeneous sample of SNe Ib/Ic light curves from the Zwicky Transient Facility. We find a systematic difference in their apparent optical colors at peak: SNe Ib are, on average, bluer than SNe Ic, with two-sample tests confirming that the distributions differ (p<0.05). The difference in their host galaxy reddening, as currently constrained, is too small to fully explain it. The color difference therefore most likely has an intrinsic origin, reflecting progenitors with different degrees of stripping -- helium-rich for SNe Ib and helium-poor for SNe Ic. In addition, we find that SNe Ib/Ic with narrow lines (SNe Ibn/Icn) are bluer than those without, which might originate from circumstellar matter interaction, with potential connection to fast blue optical transients. We demonstrate that SN colors offer a promising probe of mass stripping in massive stars, potentially providing a useful tool for analyzing large photometric data and improving predictions for the final outcomes of stripped massive stars.

astro-ph.HE↗

arXiv2025

Resonant structures in exozodiacal clouds created by exo-Earths in the habitable zone of late-type stars

Earth-like exoplanets can create resonant structures in exozodiacal dust through mean motion resonances (MMRs). These structures not only suggest the presence of such planets, but also act as potential noise sources in future mid-infrared (MIR) nulling interferometry observations. We aim to investigate how resonant structures in exozodiacal dust vary across stellar spectral types (F4--M4), and to evaluate how stellar wind drag affects their morphology and brightness in mature planetary systems. We conducted numerical simulations of dust dynamics, extending earlier studies by including spectral type variation in stellar wind drag in addition to Poynting-Robertson (PR) drag. Our models represented systems of a few Gyr hosting an Earth-like exoplanet in the habitable zone (HZ). We produced spatially resolved maps of optical depth and thermal emission for different stellar spectral types. Our simulations showed that resonant ring structures were formed for all stellar spectral types considered. In particular, we found that stellar wind drag played a critical role in shaping dust dynamics around old M-type stars, where it could dominate over PR drag by a factor of approximately 44. This reduced the contrast of resonant rings relative to the background disk, compared to cases without spectral type variation in stellar wind. Across different spectral types, the optical depth contrast of the resonant ring increased for lower-mass stars, assuming a fixed background level. Asymmetric thermal emission distributions were derived across all spectral types, which peaked for K-type stars. Our findings highlight the importance of incorporating both resonant dynamics and stellar wind effects when modeling exozodiacal dust around stars of different spectral types.

astro-ph.EP↗

arXiv2025

Near-Infrared Spectroscopy and Detection of Carbon Monoxide in the Type II Supernova SN 2023ixf

Core-collapse supernovae (CCSNe) may contribute a significant amount of dust in the early universe. Freshly formed coolant molecules (e.g., CO) and warm dust can be found in CCSNe as early as ~100 d after the explosion, allowing the study of their evolution with time series observations. In the Type II SN 2023ixf, we aim to investigate the temporal evolution of the temperature, velocity, and mass of CO and compare them with other CCSNe, exploring their implications for the dust formation in CCSNe. From observations of velocity profiles of lines of other species (e.g., H and He), we also aim to characterize and understand the interaction of the SN ejecta with preexisting circumstellar material (CSM). We present a time series of 16 near-infrared spectra of SN 2023ixf from 9 to 307 d, taken with multiple instruments: Gemini/GNIRS, Keck/NIRES, IRTF/SpeX, and MMT/MMIRS. The early (t<70 d) spectra indicate interaction between the expanding ejecta and nearby CSM. At t<20 d, intermediate-width line profiles corresponding to the ejecta-wind interaction are superposed on evolving broad P Cygni profiles. We find intermediate-width and narrow lines in the spectra until t<70 d, which suggest continued CSM interaction. We also observe and discuss high-velocity absorption features in H $α$ and H $β$ line profiles formed by CSM interaction. The spectra contain CO first overtone emission between 199 and 307 d after the explosion. We model the CO emission and find the CO to have a higher velocity (3000-3500 km/s) than that in Type II-pec SN 1987A (1800-2000 km/s) during similar phases (t=199-307 d) and a comparable CO temperature to SN 1987A. A flattened continuum at wavelengths greater than 1.5 $μ$m accompanies the CO emission, suggesting that the warm dust is likely formed in the ejecta. The warm dust masses are estimated to be on the order of ~10$^{-5} M_{\odot}$.}

astro-ph.HE↗

arXiv2025

Early Shock-Cooling Observations and Progenitor Constraints of Type IIb SN 2024uwq

We present early multi-wavelength photometric and spectroscopic observations of the Type IIb supernova SN 2024uwq, capturing its shock-cooling emission phase and double-peaked light curve evolution. Early spectra reveal broad H-alpha (v ~ 15,500 km s$^{-1}$) and He I P-Cygni profiles of similar strengths. Over time the He I lines increase in strength while the H-alpha decreases, consistent with a hydrogen envelope ($M_{env}$ = 0.7 - 1.35 $M_\odot$ ) overlying helium-rich ejecta. Analytic modeling of early shock cooling emission and bolometric light analysis constrains the progenitor to a partially stripped star with radius R = 10 - 60 $R_\odot$, consistent with a blue/yellow supergiant with an initial ZAMS mass of 12 - 20 $M_\odot$ , likely stripped via binary interaction. SN 2024uwq occupies a transitional position between compact and extended Type IIb supernovae, highlighting the role of binary mass-transfer efficiency in shaping a continuum of stripped-envelope progenitors. Our results underscore the importance of both early UV/optical observations to characterize shock breakout signatures critical to map the diversity in evolutionary pathways of massive stars. Upcoming time domain surveys including Rubin Observatory's LSST and UV missions like ULTRASAT and UVEX will revolutionise our ability to systematically capture these early signatures, probing the full diversity of stripped progenitors and their explosive endpoints.

astro-ph.HE↗

arXiv2025

"Oh FUors where art thou": A search for long-lasting YSO outbursts hiding in infrared surveys

Long-lasting episodes of high accretion can strongly impact stellar and planetary formation. However, the universality of these events during the formation of young stellar objects (YSOs) is still under debate. Accurate statistics of strong outbursts (FUors), are necessary to understand the role of episodic accretion bursts. In this work, we search for a population of FUors that may have gone undetected in the past because they either a) went into outburst before the start of modern monitoring surveys and are now slowly fading back into quiescence or b) are slow-rising outbursts that would not commonly be classified as candidate FUors. We hypothesise that the light curves of these outbursts should be well fitted by linear models with negative (declining) or positive (rising) slopes. The analysis of the infrared light curves and photometry of $\sim$99000 YSO candidates from SPICY yields 717 candidate FUors. Infrared spectroscopy of 20 candidates, from both the literature and obtained by our group, confirms that 18 YSOs are going through long-term outbursts and identifies two evolved sources as contaminants. The number of candidate FUors combined with previously measured values of the frequency of FUor outbursts, yield average outburst decay times that are 2.5 times longer than the rise times. In addition, a population of outbursts with rise timescales between 2000 and 5000 days must exist to obtain our observed number of YSOs with positive slopes. Finally, we estimate a mean burst lifetime of between 45 and 100 years.

astro-ph.SR↗

arXiv2025

Near-infrared Spectral Properties of Type Ib/Ic Supernova Progenitors and Implications for JWST and NGRST Observations

While about 20 Type II supernova progenitors have been identified using optical data from the Hubble Space Telescope (HST), direct detection of type Ib/Ic supernova (SN Ib/Ic) progenitors remains challenging due to their faint optical brightness and highly obscured environments. This study aims to investigate the detection limits and advantages of near-infrared (near-IR) observations with the James Webb Space Telescope (JWST) and the Nancy Grace Roman Space Telescope (NGRST) for the detection of SN Ib/Ic progenitors. The spectral energy distributions of SN Ib/Ic progenitor models with various masses, chemical compositions, and mass-loss rates are calculated with the non-LTE radiative transfer code CMFGEN. We then assess the detectability of SN Ib/Ic progenitors using near-IR filters from the JWST and the NGRST, comparing the results to the capabilities of the HST. Our analysis indicates that near-IR observations significantly outperform the HST in detecting SN Ib/Ic progenitors when considering the effect of extinction. Near-IR magnitudes also provide better constraints on the mass-loss rates of progenitors because of the free-free emission from the wind matter. Additionally, near-IR magnitudes and color-color diagrams are effective in distinguishing SN Ib/Ic progenitors from possible companion and/or background objects. This study suggests that the JWST and the NGRST can play a crucial role in advancing our understanding of SN Ib/Ic progenitors by improving detectability and offering better constraints on progenitor properties. We emphasize that observations with exposure times exceeding 1 hour would be needed to detect typical SNe Ib/Ic progenitors at distances greater than 10 Mpc.

astro-ph.SR↗

arXiv2024

Radio Follow-up Observations of SN 2023ixf by Japanese and Korean VLBIs

We report on radio follow-up observations of the nearby Type II supernova, SN 2023ixf, spanning from 1.7 to 269.9 days after the explosion, conducted using three very long baseline interferometers (VLBIs), which are the Japanese VLBI Network (JVN), the VLBI Exploration of Radio Astrometry (VERA), and the Korean VLBI Network (KVN). In three observation epochs (152.3, 206.1, and 269.9 days), we detected emission at the 6.9 and 8.4 GHz bands, with a flux density of $\sim 5$ mJy. The flux density reached a peak at around 206.1 days, which is longer than the timescale to reach the peak observed in typical Type II supernovae. Based on the analytical model of radio emission, our late-time detections were inferred to be due to the decreasing optical depth. In this case, the mass-loss rate of the progenitor is estimated to have increased from $\sim 10^{-6} - 10^{-5}\, M_{\odot}\,{\rm yr^{-1}}$ to $\sim 10^{-4}\, M_{\odot}\,{\rm yr^{-1}}$ between 28 and 6 years before the explosion. Our radio constraints are also consistent with the mass-loss rate to produce a confined circumstellar medium proposed by previous studies, which suggest that the mass-loss rate increased from $\sim 10^{-4}\, M_{\odot}\,{\rm yr^{-1}}$ to $\gtrsim 10^{-2}\, M_{\odot}\,{\rm yr^{-1}}$ in the last few years before the explosion.

astro-ph.HE↗

arXiv2023

The effects of Thomson scattering and chemical mixing on early-time light curves of double peaked type IIb supernovae

Previous numerical simulations of double-peaked SNe IIb light curves have demonstrated that the radius and mass of the hydrogen-rich envelope of the progenitor star can significantly influence the brightness and timescale of the early-time light curve around the first peak. In this study, we investigate how Thomson scattering and chemical mixing in the SN ejecta affect the optical light curves during the early stages of the SNe IIb using radiation hydrodynamics simulations. By comparing the results from two different numerical codes (i.e., \stella{} and \snec{}), we find that the optical brightness of the first peak can be reduced by more than a factor of 3 due to the effect of Thomson scattering that causes the thermalization depth to be located below the Rosseland-mean photosphere, compared to the corresponding case where this effect is ignored. We also observe a short-lived plateau-like feature lasting for a few days in the early-time optical light curves of our models, in contrast to typical observed SNe IIb that show a quasi-linear decrease in optical magnitudes after the first peak. A significant degree of chemical mixing between the hydrogen-rich envelope and the helium core in SN ejecta is required to reconcile this discrepancy between the model prediction and observation. Meanwhile, to properly reproduce the first peak, a significant mixing of \nifs{} into the hydrogen-rich outermost layers should be restricted. Our findings indicate that inferring the SN IIb progenitor structure from a simplified approach that ignores these two factors may introduce substantial uncertainty.

astro-ph.HE↗

arXiv2023

Near-Infrared Spectroscopy of Dense Ejecta Knots in the Outer Eastern Area of the Cassiopeia A Supernova Remnant

The Cassiopeia A supernova remnant has a complex structure, manifesting the multidimensional nature of core-collapse supernova explosions. To further understand this, we carried out near-infrared multi-object spectroscopy on the ejecta knots located in the "northeastern (NE) jet" and the "Fe K plume" regions, which are two distinct features in the outer eastern area of the remnant. Our study reveals that the knots exhibit varying ratios of [S II] 1.03 $μ$m, [P II] 1.189 $μ$m, and [Fe II] 1.257 $μ$m lines depending on their locations within the remnant, suggesting regional differences in elemental composition. Notably, the knots in the NE jet are mostly 'S-rich' with weak or no [P II] lines, implying that they originated below the explosive Ne burning layer, consistent with the results of previous studies. We detected no ejecta knots exhibiting only [Fe II] lines in the NE jet area that are expected in the jet-driven SN explosion model. Instead, we discovered a dozen 'Fe-rich' knots in the Fe K plume area. We propose that they are dense knots produced by a complete Si burning with $α$-rich freezeout in the innermost region of the progenitor and ejected with the diffuse X-ray emitting Fe ejecta but decoupled after crossing the reverse shock. In addition to these metal-rich ejecta knots, several knots emitting only He I 1.083 $μ$m lines were detected, and their origin remains unclear. We also detected three extended H emission features of circumstellar or interstellar origin in this area and discuss its association with the supernova remnant.

astro-ph.HE↗

arXiv2023

Optical color of Type Ib and Ic supernovae and implications for their progenitors

Type Ib and Ic supernovae (SNe Ib/Ic) originate from hydrogen-deficient massive star progenitors, of which the exact properties are still much debated. Using the SN data in the literature, we investigate the optical $B-V$ color of SNe Ib/Ic at the $V-$band peak and show that SNe Ib are systematically bluer than SNe Ic. We construct SN models from helium-rich and helium-poor progenitors of various masses using the radiation hydrodynamics code STELLA and discuss how the $B-V$ color at the $V-$band peak is affected by $^{56}$Ni to ejecta mass ratios, $^{56}$Ni mixing and presence/absence of the helium envelope. We argue that the dichotomy in the amounts of helium in the progenitors plays the primary role in making the observed systematic color difference at the optical peak, in favor of the most commonly invoked SN scenario that SNe Ib and SNe Ic progenitors are helium-rich and helium-poor, respectively.

astro-ph.SR↗

arXiv2023

Near-Infrared and Optical Observations of Type Ic SN 2021krf: Luminous Late-time Emission and Dust Formation

We present near-infrared (NIR) and optical observations of the Type Ic supernova (SN Ic) SN 2021krf obtained between days 13 and 259 at several ground-based telescopes. The NIR spectrum at day 68 exhibits a rising $K$-band continuum flux density longward of $\sim$ 2.0 $μ$m, and a late-time optical spectrum at day 259 shows strong [O I] 6300 and 6364 Å emission-line asymmetry, both indicating the presence of dust, likely formed in the SN ejecta. We estimate a carbon-grain dust mass of $\sim$ 2 $\times$ 10$^{-5}$ M$_{\odot}$ and a dust temperature of $\sim$ 900 - 1200 K associated with this rising continuum and suggest the dust has formed in SN ejecta. Utilizing the one-dimensional multigroup radiation hydrodynamics code STELLA, we present two degenerate progenitor solutions for SN 2021krf, characterized by C-O star masses of 3.93 and 5.74 M$_{\odot}$, but with the same best-fit $^{56}$Ni mass of 0.11 M$_{\odot}$ for early times (0-70 days). At late times (70-300 days), optical light curves of SN 2021krf decline substantially more slowly than that expected from $^{56}$Co radioactive decay. Lack of H and He lines in the late-time SN spectrum suggests the absence of significant interaction of the ejecta with the circumstellar medium. We reproduce the entire bolometric light curve with a combination of radioactive decay and an additional powering source in the form of a central engine of a millisecond pulsar with a magnetic field smaller than that of a typical magnetar.

astro-ph.HE↗

arXiv2023

He abundance of Dense Circumstellar Clumps in the Cassiopeia A Supernova Remnant

We report on the result of He abundance analysis of dense circumstellar clumps in the young supernova remnant Cassiopeia A. These clumps, which are called quasi-stationary flocculi (QSFs), are known from previous optical studies to be enriched in He along with N, but the degree of He overabundance relative to H has remained uncertain. For several QSFs with near-infrared spectroscopic data, we have analyzed their He I 1.083 $μ$m/Pa$γ$ ratios together with the ratios of [Fe II] lines by using the Raymond shock code. According to our analysis, He is overabundant relative to H by a factor of $\lesssim 3$ in most of these QSFs. This He abundance of QSFs is consistent with the previous conclusion from the N overabundance that QSFs were ejected when a substantial amount of the H envelope of the progenitor star had been stripped off. We discuss the mass-loss history of the progenitor star and the origin of QSFs.

astro-ph.SR↗

arXiv2023

The Early Light Curve of a Type Ia Supernova 2021hpr in NGC 3147: Progenitor Constraints with the Companion Interaction Model

The progenitor system of Type Ia supernovae (SNe Ia) is expected to be a close binary system of a carbon/oxygen white dwarf (WD) and a non-degenerate star or another WD. Here, we present results from a high-cadence monitoring observation of SN 2021hpr in a spiral galaxy, NGC 3147, and constraints on the progenitor system based on its early multi-color light curve data. First, we classify SN 2021hpr as a normal SN Ia from its long-term photometric and spectroscopic data. More interestingly, we found a significant "early excess" in the light curve over a simple power-law $\sim t^{2}$ evolution. The early light curve evolves from blue to red and blue during the first week. To explain this, we fitted the early part of $BVRI$-band light curves with a two-component model of the ejecta-companion interaction and a simple power-law model. The early excess and its color can be explained by shock cooling emission due to a companion star having a radius of $8.84\pm0.58$$R_{\odot}$. We also examined HST pre-explosion images with no detection of a progenitor candidate, consistent with the above result. However, we could not detect signs of a significant amount of the stripped mass from a non-degenerate companion star ($\lesssim0.003\,M_{\odot}$ for H$α$ emission). The early excess light in the multi-band light curve supports a non-degenerate companion in the progenitor system of SN 2021hpr. At the same time, the non-detection of emission lines opens a door for other methods to explain this event.

astro-ph.SR↗

arXiv2022

Red supergiant stars in IC 1613 and metallicity-dependent mixing length in the evolutionary model

We report a spectroscopic study on red supergiant stars (RSGs) in the irregular dwarf galaxy IC 1613 in the Local Group. We derive the effective temperatures ($T_\mathrm{eff}$) and metallicities of 14 RSGs by synthetic spectral fitting to the spectra observed with the MMIRS instrument on the MMT telescope for a wavelength range from 1.16 $μ$m to 1.23 $μ$m. A weak bimodal distribution of the RSG metallicity centered on the [Fe/H]=$-0.65$ is found, which is slightly lower than or comparable to that of the Small Magellanic Cloud (SMC). There is no evidence for spatial segregation between the metal rich ([Fe/H]$>-0.65$) and poor ([Fe/H]$<-0.65$) RSGs throughout the galaxy. The mean effective temperature of our RSG sample in IC 1613 is higher by about 250 K than that of the SMC. However, no correlation between $T_\mathrm{eff}$ and metallicity within our RSG sample is found. We calibrate the convective mixing length ($α_{\mathrm{MLT}}$) by comparing stellar evolutionary tracks with the RSG positions on the HR diagram, finding that models with $α_{\mathrm{MLT}}=2.2-2.4 H_P$ can best reproduce the effective temperatures of the RSGs in IC 1613 for both Schwarzschild and Ledoux convection criteria. This result supports our previous study that a metallicity dependent mixing length is needed to explain the RSG temperatures observed in the Local Group, but we find that this dependency becomes relatively weak for RSGs having a metallicity equal to or less than the SMC metallicity.

astro-ph.GA↗

arXiv2022

Mass loss of massive helium star supernova progenitors shortly before explosion constrained by supernova radio properties

Mass loss of massive helium stars is not well understood even though it plays an essential role in determining their remnant neutron-star or black-hole masses as well as ejecta mass of Type Ibc supernovae. Radio emission from Type Ibc supernovae is strongly affected by circumstellar matter properties formed by mass loss of their massive helium star progenitors. In this study, we estimate the rise time and peak luminosity distributions of Type Ibc supernovae in radio based on a few massive helium star mass-loss prescriptions and compare them with the observed distribution to constrain the uncertain massive helium star mass-loss rates. We find that massive helium stars in the luminosity range expected for ordinary Type Ibc supernova progenitors (4.6 ~< log L/Lsun ~< 5.2) should generally have large mass-loss rates (> ~ 1e-6 Msun/yr) in order to account for the observed rise time and peak luminosity distribution. Therefore, mass-loss prescriptions that predict significantly low mass-loss rates for helium stars in this luminosity range is inconsistent with the supernova radio observations. It is also possible that massive helium stars shortly before their explosion generally undergo mass-loss enhancement in a different way from the standard radiation-driven wind mechanism.

astro-ph.SR↗

arXiv2022

Stripped-envelope stars in different metallicity environments. II. Type I supernovae and compact remnants

Stripped-envelope stars can be observed as Wolf-Rayet (WR) stars, or as less luminous hydrogen-poor stars with low mass loss rates and transparent winds. Both types are potential progenitors of Type I core-collapse supernovae (SNe). We use grids of core-collapse models obtained from helium stars at different metallicities to study the effects of metallicity on the transients and remnants these stars produce. We characterise the surface and core properties of our core collapse models, and investigate their explodability employing three criteria. In cases where explosions are predicted, we estimate the ejecta mass, explosion energy, nickel mass and neutron star (NS) mass. Otherwise, we predict the mass of the resulting black hole (BH). We construct a simplified population model, and find that the properties SNe and compact objects depend strongly on metallicity. Ejecta masses and explosion energies for Type Ic SNe are best reproduced by models with Z=0.04 which exhibit strong winds during core helium burning. This implies that either their mass loss rates are underestimated, or that Type Ic SN progenitors experience mass loss through other mechanisms before exploding. The distributions of ejecta masses, explosion energies and nickel mass for Type Ib SNe are not well reproduced by progenitor models with WR mass loss, but are better reproduced if we assume no mass loss in progenitors with luminosities below the minimum WR star luminosity. We find that Type Ic SNe become more common as metallicity increases, and that the vast majority of progenitors of Type Ib SNe must be transparent-wind stripped-envelope stars. We find several models with pre-collapse CO-masses of up to $\sim 30 M_{\odot}$ may form $\sim 3 M_{\odot}$ BHs in fallback SNe. This may carry important consequences for our understanding of SNe, binary BH and NS systems, X-ray binary systems and gravitational wave transients.

astro-ph.SR↗

arXiv2022

Effects of Winds on the Optical Properties of Type Ib and Ic Supernova Progenitors

We investigate the effects of winds on the observational properties of Type Ib and Ic supernova (SN Ib/Ic) progenitors using spectral models constructed with the non-LTE stellar atmospheric code CMFGEN. We consider SN Ib/Ic progenitor models of the final mass range of 2.16 -- 9.09~$M_\odot$ having different surface temperatures and chemical compositions, and calculate the resulting spectra for various wind mass-loss rates and wind terminal velocities. We find that the progenitors having an optically thick wind would become brighter in the optical for a higher mass-loss rate (or a lower wind terminal velocity), because of the formation of the photosphere in the extended wind matter and the contribution from free-free and line emissions from the wind. As a result, for the standard Wolf-Rayet wind mass-loss rate, helium-deficient compact SN Ic progenitors would be brighter in the optical by $\sim$3 mag compared to the case without the wind effects. We also find that the color dependence on the photospheric temperature is non-monotonic because of the wind effects. Our results imply that inferring the progenitor mass, bolometric luminosity and effective temperature from the optical observation using the standard stellar evolution model prediction can be misleading. By comparing our fiducial model predictions with the detection limits of the previous SN Ib/Ic progenitor searches, we conclude that a deep search with an optical absolute magnitude larger than $\sim -4$ is needed to directly identify most of the ordinary SN Ib/Ic progenitors. We discuss implications of our results for the observed SN Ib/Ic progenitor candidates for iPTF13bvn, SN 2019yvr and SN 2017ein.

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