Unveiling the Dual Nature of V1180 Cas: UXor-like Dips and EXor-like Bursts Across a Decade

TL;DR

V1180 Cas exhibits a dual-mode variability, blending UXor-like extinction-driven dips with EXor-like accretion bursts. The study combines a long-term, multi-band photometric time series (1999–2025) with extensive optical–NIR spectroscopy (0.5–2.5 μm) to diagnose how circumstellar extinction, inner-disk heating, and magnetospheric accretion drive the observed brightness changes. Key findings include eleven quasi-periodic dips since 2018, color changes implying both scattering and thermal disk evolution, and persistent emission lines tracing ongoing accretion and outflows; accretion rates peak at ~10^{-7} M_⊙ yr^{-1} and correlate negatively with optical magnitude via a slope of about -0.47 M_⊙ yr^{-1} mag^{-1}, while outflows show \,dot{M}_{out} ~ 1.2×10^{-8} M_⊙ yr^{-1} and electron densities n_e ~ 4×10^3 cm^{-3}. The results indicate a coupled, evolving inner disk structure where extinction and accretion/outflow processes co-vary, a scenario consistent with a hybrid UXor/EXor evolutionary path for a young stellar object. The work demonstrates the power of coordinated, multi-wavelength monitoring to dissect the complex circumstellar environments of eruptive YSOs and informs models of episodic accretion and disk winds in early stellar evolution.

Abstract

We present a detailed analysis of the long-term photometric and spectroscopic evolution of V1180 Cas over a decade, aiming to identify the dominant mechanisms behind its variability. We combine multi-band light curves from 1999 to 2025 with over 30 epochs of optical to near-infrared spectroscopy (0.5-2.5 $μ$m), analyzing variability patterns, color behavior, and emission line diagnostics. We investigate the temporal evolution of accretion and outflow indicators and their correlation with photometric states. The light curve reveals a transition from sporadic early dimming events to a quasi-periodic pattern since 2018, with eleven major dips showing asymmetry and stochastic sub-structure. Color-magnitude diagrams show classic UXor-like blueing during deep minima, while near-infrared and mid-infrared color changes indicate thermal evolution of disk. Spectroscopic analysis reveals persistent hydrogen, Ca II, He I, and forbidden line emission. Accretion diagnostics track photometric variability, and forbidden lines often intensify during dips, implying a physical link between extinction and outflows. Estimated accretion rates range from $\sim10^{-8}-10^{-7}$ $M_\odot$yr$^{-1}$; the outflow rate and density diagnostics are consistent with disk winds and shock-excited jets. V1180 Cas demonstrates dual-mode variability driven by both variable circumstellar extinction and episodic accretion events. The hybrid UXor/EXor behavior, combined with evolving disk signatures and persistent outflows, suggests a young stellar object undergoing coupled accretion-extinction-outflow evolution. Continued monitoring will be essential to fully resolve the physical processes shaping its variability.

Figures (14)

• Figure 1: Left panel: Color-composite image obtained using the $W4$ (22 $\mu$m), $W3$ (12 $\mu$m), and $W2$ (4.6 $\mu$m) WISE images, shown as red, green, and blue colors, respectively. The Field of View (FoV) of this color-composite image is $\sim$10$^{\prime}$$\times$ 10$^{\prime}$ around the V1180 Cas. The cyan color box shows the FoV of TANSPEC. Right panel: The color-composite image comprises TANSPEC $K$, $H$, and $J$ band images shown as red, green, and blue, respectively. The cyan circle shows the location of the V1180 Cas, while reference stars, which are used to calculate offsets to calibrate the instrumental magnitudes (see Section \ref{['subsubsec:observed']}), are marked with green circles.
• Figure 2: Upper panel: The historical $I$-band LC of V1180 Cas, covering the full range of previously published data from 1999 to 2022, is presented to highlight the source's long-term photometric variability. The data spanning 1999–2011 and 2011–2022 are taken from Kun_2011 and Mutafov_2022RAA....22l5014M, respectively. The 7 dips reported in previous studies are marked using black arrows and labeled as D1, D2, and so on. The shaded region highlights our monitoring period. Lower panel: The LC of V1180 Cas, combining catalog data and currently observed data. Catalog data includes ZTF , $zr$, Gaia DR3 $G_{RP}$, and ATLAS $o$. The current dataset consists of $R$-band observations obtained with HFOSC and DFOT. The vertical solid lines, colored blue, green, and red, represent the epochs of spectroscopic data, taken with HFOSC G7, HFOSC G8, and TANSPEC, respectively. The linear trends during fading and brightening events are marked using black dashed lines, and their slope (mag day$^{-1}$) values are shows in the lower sub-panel (for details, see Section \ref{['sec:res_lc_ro']}). All the large dips are marked with black arrows and labeled. In both panels, vertical dashed grey lines correspond to January 1st of each year, labeled on the upper x-axis. (The currently observed data used in this figure are available.)
• Figure 3: The ZTF $zr$ band data, featuring high cadence (2-3 days) and regular observations between MJD 58665 and 58820 (D7), displays periodic variability in the LC. The upper panel illustrates the power spectrum for data (blue) and window function (red), obtained using a GLS periodogram. The red horizontal dotted lines indicate the 1$\%$ and 10$\%$ false alarm probability levels. The most significant peak is highlighted with a grey dashed vertical line. The lower panel shows the phase-folded LC using a period of 29.2 days, which corresponds to the most prominent peak in the power spectrum. The red curve in the lower panel shows a sine curve with a period of 29.2 days.
• Figure 4: The optical, MIR color, and extinction ($A_V$) variation across different epochs. Upper panel: Shows the optical color evolution of V1880 Cas using ZTF ($zg$, $zr$), ATLAS ($c$, $o$) and GAIA DR3 ($G_{BP}$, $G_{RP}$) data. Circles denote ZTF $zr$ mag color-coded by ($zg - zr$), star symbols represent Gaia $G_{RP}$ mag color-coded by ($G_{BP} - G_{RP}$), and squares indicate ATLAS $o$-band data color-coded by ($c - o$). The dips identified in the lower panel of Figure \ref{['fig:lc_all']} are also marked here. Middle panel: The $A_V$ variation across different epochs with color coded using $\Delta A_V$ values. The $\Delta A_V$ values are calculated using color-color ($V-R$ versus $R-I$) diagram, using data from Mutafov_2022RAA....22l5014M. Lower panel: The LC using NEOWISE W1 data, color represents W1-W2 color. Black circles represent the median values of nearby observations (within 30 days).
• Figure 5: Upper panels: CMD of V1180 Cas using ZTF ($zg$ and $zr$) and NEOWISE ($W1$ and $W2$) data, color represents observation epoch (in years) in both panels. The left panel shows $zr$ mag vs. ($zg-zr$) color. The right panel shows the MIR CMD, $W1$ vs. $W1$-$W2$. The grey data points are actual observations, while the black circles denote median values of nearby (within 30 days) observations. The black arrows in both panels show the extinction vector, and the red "+" sign denotes the $A_V$ difference of 1 mag in the optical CMD ($zr$ vs. $zr-zg$) and 5 mag in the MIR CMD ($W1$ vs. $W1$-$W2$). Lower panels: The CMD (left) and color-color diagram (right) using $J$, $H$, and $K$ bands photometric data. The square data points represent the data from the literature Kun_2011Antoniucci_2014AA...565L...7A, and the circles represent data observed from TANSPEC. In the left panel, the black arrow represents the extinction vector with marked 5 mag differences in $A_V$ as a red "+" sign. In the right panel, the solid curve shows the locus of field dwarfs, and the dotted curve shows the locus of giants Bessell_1988PASP..100.1134B. The dotted line represents the locus of classical T-Tauri (CTT) stars Meyer_1997AJ....114..288M. The diagonal straight dashed lines show the reddening vectors Rieke_1985ApJ...288..618R, with red "+" signs denoting an $A_V$ difference of 5 mag. The color-code represents the observation epochs (MM/YYYY) labeled on the right side of the figures. (The TANSPEC data used in this figure are available.)