Classical T Tauri stars with VPHAS$+$: I: H$\alpha$ and $u$-band accretion rates in the Lagoon Nebula M8

TL;DR

This study estimates accretion rates of 235 Classical T Tauri stars in the Lagoon Nebula using VPHAS+ photometry, revealing spatial distribution patterns and accretion rate variations consistent with star formation processes.

Contribution

First large-scale photometric estimation of accretion rates for CTTS in the Lagoon Nebula, combining Hα and u-band data to analyze spatial and accretion properties.

Findings

Accretion rates vary by about 0.17 dex between methods.

Strong accretors are spatially concentrated, weak ones are more dispersed.

Results challenge previous sequential star formation models.

Abstract

We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using $ugri$H$\alpha$ photometry from the VPHAS+ survey. Our sample consists of stars displaying H$\alpha$-excess, the intensity of which is used to derive accretion rates. For a subset of 87 stars, the intensity of the $u$-band excess is also used to estimate accretion rates. We find the mean variation in accretion rates measured using H$\alpha$ and $u$-band intensities to be $\sim$ 0.17 dex, agreeing with previous estimates (0.04-0.4 dex) but for a much larger sample. The spatial distribution of CTTS align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. Strong accretors are concentrated spatially, while weak accretors are more distributed. Our results do not support the sequential star forming processes suggested in the literature.