Identification of red supergiants in the Local Group with mid-IR photometry Nikolay Britavskiy NOA supervisor: Dr. Alceste Bonanos Collaborators: S. Williams, A. Mehner, M. Boyer, D. Garcia, J. Prieto

Motivation RSGs are from Davies et al. (2013) 1. Different temperature scales 2. Discrepancy in evolutionary models 3. Metallicity effect

Our goals: Increase the number of spectroscopically confirmed RSGs in metal poor dIrr galaxies in the Local Group. Estimate the physical parameters of newly identified RSGs. Our technique: Use Spitzer archival data. Use selection criteria based on work of Bonanos et al. (2009, 2010) Confirm RSG candidates with follow-up spectroscopy. DUST In Nearby Galaxies with Spitzer survey (DUSTiNGS, Boyer et al. 2015b)

Mid-IR selection criteria Spectroscopically confirmed population of massive stars in the LMC and SMC (Bonanos et al. 2009, 2010) RSGs sgB[e]

Mid-IR selection criteria Spectroscopically confirmed population of massive stars in the LMC and SMC (Bonanos et al. 2009, 2010) RSGs sgB[e] RSGs sgB[e]

7 dIrr galaxies (13 in total) in the Local Group with high star formation rate: Program galaxies Sextans A 15 targets Sextans B 5 targets WLM 31 targets Phoenix 14 targets IC targets Pegasus 19 targets IC targets Total: 104 candidates

Observations Longslit and multi-object spectroscopy modes on: GTC - OSIRIS (2014B, 10.6h) Du Pont - WFCCD (J. Prieto) ESO/VLT - FORS2 (P90/P91, 11h + 3.4h) Resolution R ≤ 1000 Signal-to-Noise:

Discovery of new RSGs Radial velocity Cross correlation of Ca II triplet Spectral type Fitting of TiO bands Luminosity class Fitting of Ca II triplet TiO Ca II

Results in WLM sgB[e] RSGs

Results in WLM (Spectral variability of RSGs) sgB[e] RSGs RSGs are from Levesque & Massey (2012)

Results in WLM (Iron stars)

Results in WLM (Carbon stars)

Survey Results Britavskiy et al. (2014) Britavskiy et al. (A&A, submitted) Britavskiy et al. (in prep.)

Next steps: 1.Measure the physical parameters (radius, effective temperature, gravity, metallicity) of newly identified RSGs. 2. Compare their position on the H-R diagram with evolutionary models.

TiO fitting with a MARCS models

New RSGs on the H-R diagram 1.Get the physical parameters of newly identified RSGs, such as: Radius, effective temperature, gravity, metallicity … 2. Compare their position on the H-R diagram with evolutionary models. 3. Complete the census of RSGs in the star forming dIrrs in the Local Group (we expect to receive more VLT/FORS2 spectra from WLM during the P95 semester). Preliminary

Summary 1.We identified 25 RSGs (21 new discoveries) and 2 emission line objects in 7 star-forming dIrrs galaxies in the Local Group. 2.We demonstrated success of identifying dusty massive stars in the Local Group with Spitzer mid-IR photometry. 3.We revised the optical and mid-IR selection criteria for RSGs. 4.The census of RSGs in WLM will be completed during P95 run at VLT/FORS2. This work increased the sample of spectroscopically confirmed RSGs in dIrr galaxies in the Local Group by 21 (47 %).

Thank you! Visit the poster of Dr. S. Williams :) FM16 p.12

Mid-IR selection criteria for RSGs RSGs region [3.6]-[4.5] < 0; This study + RSGs in NGC 6822 (Levesque & Massey, 2012)

Optical selection criteria for RSGs Massey et al Levesque & Massey, 2012