Historical Surveys to Rubin First Look: Absolute Colors of trans-Neptunian objects

Abstract

We present a comprehensive photometric study of transNeptunian objects (TNOs) by combining data from SDSS, Col-OSSOS, DES, and the recent Rubin First Look (RFL) data. Our database comprises 43 878 measurements in the u, g, r, i, z, and J filters, from which we derived 8 738 phase curves for 1 921 unique objects. From these data, we computed 12 852 absolute color measurements and spectral slope differences for 1 761 objects, allowing a statistical characterization of phase coloring effects. The colors show no strong bimodality or correlation with orbital parameters, emphasizing the importance of phase correction even for small phase angles. The increase in sample size and application of phase corrections fill previously empty regions in color magnitude space likely affected by observational biases, as redder (and thus darker) objects are preferentially lost near detection limits. Notably, our dataset includes the first photometric measurements from Rubin Observatory during RFL, covering eight objects (five newly discovered TNOs and three previously known). These early LSST observations occupy sparsely sampled regions of parameter space, particularly at faint magnitudes, highlighting the discovery and characterization potential of the full survey. We confirm previous results showing that TNO colors vary with phase angle, exhibiting both reddening and bluening trends. Correlations between (dS'/dalpha) and (alpha) strengthen with increasing (Delta lambda), except for Hi - Hz, which tends to neutralize, consistent with the spectral flattening previously reported in visible wavelengths.

Figures (12)

• Figure 1: Number of observations per photometric filter in the combined TNO catalog. The filters $u$, $g$, $r$, $i$, $z$, and $J$ are shown with distinct colors. The numeric labels above each bar indicate the exact number of observations for that filter.
• Figure 2: Phase angle coverage for the TNOs in the combined catalog. The x-axis shows the minimum observed phase angle, $\alpha_\mathrm{min}$, and the y-axis shows the phase angle range, $\Delta \alpha = \alpha_\mathrm{max} - \alpha_\mathrm{min}$. The color scale indicates the number of TNOs in each bin.
• Figure 3: Median rotational amplitude as a function of absolute magnitude. Black points show individual TNO amplitudes reported in the LCDB, while the red line represents the median $\Delta m$(H) curve obtained by binning the data into 13 equally sized bins in H.
• Figure 4: Example phase-curve fitting for a single TNO (2006 QF181) across different filters. Left panels: Observed reduced magnitudes versus phase angle for different surveys (markers indicate survey origin), with the median linear fit overplotted in a solid line. Right panels: Two-dimensional histogram of 2000 Monte Carlo iterations of the linear fit, showing the distribution of phase slope ($\mathrm{\beta}$) versus absolute magnitude ($\mathrm{H}$).
• Figure 5: Distributions of the median phase slope parameter ($\beta_{\mathrm{median}}$) and absolute magnitude ($H_{\mathrm{median}}$) for our sample. Red dashed and purple solid lines mark the mean and median values. Extreme phase slopes ($|\beta| > 1.5~\mathrm{mag~deg^{-1}}$) have been excluded.