New optically identified supernova remnants in the Large Magellanic Cloud

ABSTRACT We present a new optical sample of three Supernova Remnants (SNRs) and 16 Supernova Remnant (SNR) candidates in the Large Magellanic Cloud (LMC). These objects were originally selected using deep H α, [S ii], and [O iii] narrow-band imaging. Most of the newly found objects are located in less dense regions, near or around the edges of the LMC’s main body. Together with previously suggested MCSNR J0541–6659, we confirm the SNR nature for two additional new objects: MCSNR J0522–6740 and MCSNR J0542–7104. Spectroscopic follow-up observations for 12 of the LMC objects confirm high [S ii]/H α emission-line ratios ranging from 0.5 to 1.1. We consider the candidate J0509–6402 to be a special example of the remnant of a possible type Ia Supernova (SN) which is situated some 2° (∼1.75 kpc) north from the main body of the LMC. We also find that the SNR candidates in our sample are significantly larger in size than the currently known LMC SNRs by a factor of ∼2. This could potentially imply that we are discovering a previously unknown but predicted, older class of large LMC SNRs that are only visible optically. Finally, we suggest that most of these LMC SNRs are residing in a very rarefied environment towards the end of their evolutionary span where they become less visible to radio and X-ray telescopes.

Dust Emission in Early-Type Galaxies with the Herschel Virgo Cluster Survey

We have searched for dust in an optical sample of 910 Early-Type Galaxies (ETGs) in the Virgo cluster (447 of which are optically complete at mpg ≤ 18.0), extending also to the dwarf ETGs, using Herschel images at 100, 160, 250, 350 and 500 μm. Dust was found in 52 ETGs (46 are in the optically complete sample), including M87 and another 3 ETGs with strong synchrotron emisssion. Dust is detected in 17% of ellipticals, 41% of lenticulars, and in about 4% of dwarf ETGs. The dust-to-stars mass ratio increases with decreasing optical luminosity, and for some dwarf ETGs reaches values similar to those of the dusty late-type galaxies. Slowly rotating ETGs are more likely to contain dust than fast rotating ones. Only 8 ETGs have both dust and HI, while 39 have only dust and 8 have only HI, surprisingly showing that only rarely dust and HI survive together. ETGs with dust appear to be concentrated in the densest regions of the cluster, while those with HI tend to be at the periphery. ETGs with an X-ray active SMBH are more likely to have dust and vice versa the dusty ETGs are more likely to have an active SMBH.

Determining the Thickness and Refractive Index of a Birefringence by Using an Improved Accurate Measurement System

This paper presents a high-precision, non-destructive measurement system for determining the thickness and refractive indices of birefringent optical wave plates. Significantly, the proposed method enables the two refractive indices of the optical sample to be measured simultaneously. The performance of the proposed system is verified using a commercial quartz optical wave plate with known refractive indices of 1.5518 e n = and 1.5427 o n = , respectively, and a thickness of 452.1428 μm. The experimentally determined values of the refractive indices are found to be 1.55190 e n = and 1.54281 o n = , respectively, while the thickness is found to be 452.189 μm, corresponding to an experimental error of approximately 0.046 μm. The measurement resolution of the proposed system exceeds that of the interferometer hardware itself and provides a simple yet highly accurate means of measuring the principal optical parameters of birefringent glass wave plates.