mollwollfumble said:
Tau.Neutrino said:
ALMA’s highest frequency receiver produces its first scientific result on massive star formation
The Atacama Large Millimeter/submillimeter Array (ALMA) has tuned in another new channel for signals from space. Using its highest frequency receivers yet, researchers obtained 695 radio signatures for various molecules, including simple sugar, in the direction of a massive star forming region. These first scientific results from the ALMA Band 10 receivers developed in Japan ensure a promising future for high frequency observations.
Read more at: https://phys.org/news/2018-11-alma-highest-frequency-scientific-result.html#jCp
> The ALMA observations detected more than ten times as many spectral lines as the Herschel data.
I’m going to have to think about this. I thought that Herschel was a great instrument.
The name
ALMA just struck me as funny. The “LM” stands for “large millimetre”, just what is a “large millimetre”?
OK. Let me think about it. My understanding is that these are wavelengths near the borderline between infrared and microwave. Therefore very difficult to observe on Earth because of the heat of the ground and atmosphere. Hence the space observations, in a location far from Earth. Let me check that.
Herschel was a “Far Infrared and Submillimetre Telescope. Wavelengths 55 to 672 µm”.
ALMA “operates at wavelengths of 9.6 to 0.3 millimeters”. ALMA’s Band 10 is 787 to 950 GHz, which translates to 310 to 380 µm. That’s well within Hershel’s range. “astronomers sometimes define far infrared as wavelengths between 25 µm and 350 µm”. So ALMA’s Band 10 really straddles the borderline between infrared and microwave.
The band is affected by heat, a bit. “Objects with temperatures between about 5 K and 340 K will emit radiation in the far infrared range”. The cosmic microwave background emits at longer wavelengths, near 160 GHz and 1 mm. This is the cosmic infrared background, but this does not include the contribution from Earth.
The following is more relevant. The Earth’s atmosphere absorbs nearly all the incident radiation at wavelengths between 20 and 500 micrometres. So we expect ALMA’s band 10 near 350 micrometres to be up the creek without much of a paddle.
The article suggests that ALMA’s Band 10 is ideal for identifying interstellar organic molecules. “The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher-energy near-IR, approximately 14000–4000 cm−1 (0.8–2.5 μm wavelength) can excite overtone or harmonic vibrations. The mid-infrared, approximately 4000–400 cm−1 (2.5–25 μm) may be used to study the fundamental vibrations and associated rotational-vibrational structure. The far-infrared, approximately 400–10 cm−1 (25–1000 μm), lying adjacent to the microwave region, has low energy and may be used for rotational spectroscopy.”
> But whereas Herschel detected 65 molecular emission lines, ALMA detected 695.
My tentative conclusion. We need to be darn careful to ensure that those extra emission lines come from outside the Earth’s atmosphere. Without extreme quality control, all they would be picking up would be molecules in the Earth’s atmosphere. This is a valuable scientific result in itself, but not an astronomical one.