Starship Asterisk*

Chris Peterson wrote: ↑Wed Jan 19, 2022 5:48 pm

neufer wrote: ↑Wed Jan 19, 2022 4:00 pm

Chris Peterson wrote: ↑Tue Jan 18, 2022 8:32 pm
My guess is that the illumination here is external. Dust reflecting starlight.

Antares can barely light up its own local dust cloud: https://apod.nasa.gov/apod/ap190827.html

Looks VERY lit up to me!

neufer wrote: ↑Wed Jan 19, 2022 4:00 pm

Chris Peterson wrote: ↑Tue Jan 18, 2022 8:32 pm

neufer wrote: ↑Tue Jan 18, 2022 8:25 pm
In any event, do you think that the illumination here is due to embedded T Tauri stars?

My guess is that the illumination here is external. Dust reflecting starlight.

Antares can barely light up its own local dust cloud: https://apod.nasa.gov/apod/ap190827.html

Chris Peterson wrote: ↑Tue Jan 18, 2022 8:32 pm

neufer wrote: ↑Tue Jan 18, 2022 8:25 pm
In any event, do you think that the illumination here is due to embedded T Tauri stars?

My guess is that the illumination here is external. Dust reflecting starlight.

jarmoruuth wrote: ↑Tue Jan 18, 2022 9:39 pm Images were taken with a remote system and filters are listed as Astrodon LRGB 2GEN 50mm square. I am not an expert on this matter but I assume it is a normal LRGB setup.

neufer wrote: ↑Tue Jan 18, 2022 8:25 pm

Chris Peterson wrote: ↑Tue Jan 18, 2022 5:42 pm

neufer wrote: ↑Tue Jan 18, 2022 5:37 pm
So is this near-IR APOD image allowing us to detect scattered near-IR light from cool but luminous internal T Tauri stars :?:

This was imaged through (presumably) conventional LRGB filters, which block near-IR which would otherwise mess up "natural" colors. I don't think there's any IR being captured here.

(Another semantics standoff. :| ) Well... Optolong LRGB Filter spectrum diagram extends up to 745 nanometers.

https://en.wikipedia.org/wiki/Infrared wrote:
<<Infrared (IR) is generally understood to encompass wavelengths from around 1 millimeter
to the nominal red edge of the visible spectrum, around 700 nanometers.>>

• In any event, do you think that the illumination here is due to embedded T Tauri stars?

Chris Peterson wrote: ↑Tue Jan 18, 2022 5:42 pm

neufer wrote: ↑Tue Jan 18, 2022 5:37 pm
So is this near-IR APOD image allowing us to detect scattered near-IR light from cool but luminous internal T Tauri stars

This was imaged through (presumably) conventional LRGB filters, which block near-IR which would otherwise mess up "natural" colors. I don't think there's any IR being captured here.

https://en.wikipedia.org/wiki/Infrared wrote:
<<Infrared (IR) is generally understood to encompass wavelengths from around 1 millimeter
to the nominal red edge of the visible spectrum, around 700 nanometers.>>

• In any event, do you think that the illumination here is due to embedded T Tauri stars?

neufer wrote: ↑Tue Jan 18, 2022 5:37 pm So is this near-IR APOD image allowing us to detect scattered near-IR light from cool but luminous internal T Tauri stars :?:

Chris Peterson wrote: ↑Tue Jan 18, 2022 4:33 pm

johnnydeep wrote: ↑Tue Jan 18, 2022 3:56 pm

neufer wrote: ↑Mon Jan 17, 2022 10:55 pm
The Earth radiates ~10 micrometers. I would imagine that the dust here is much cooler than the Earth.

https://apod.nasa.gov/apod/ap090715.html

According to Wien's Law, stuff at 300 K has a black body radiation spectrum with a peak at 2898 μm⋅K / 300 K = 9.66 μm (micrometers), which is in the IR.

So the question is: just how hot is this interstellar dust?

The dust in fairly dense dark nebulas like this can range in temperature from about 10 K to about 100 K, depending on how much star formation is taking place in them and how many hot stars are in their vicinity. Based on the amount of light we see reflected (with considerably more absorbed), I'd suspect we're looking at the higher end of this range, which would argue for a radiation peak in the 30-50 μm range, or mid-IR.

• So is this near-IR APOD image allowing us to detect scattered near-IR light from cool but luminous internal T Tauri stars

https://en.wikipedia.org/wiki/Chamaeleon wrote:
<<The Chamaeleon constellation contains a number of molecular clouds (the Chamaeleon dark clouds) that are forming low-mass T Tauri stars. The cloud contains tens of thousands of solar masses of gas and dust. T Tauri stars (TTS) are a class of variable stars that are less than about ten million years old. They are found near molecular clouds and identified by their optical variability and strong chromospheric lines. T Tauri stars are pre-main-sequence stars in the process of contracting to the main sequence along the Hayashi track, a luminosity–temperature relationship obeyed by infant stars of less than 3 M_☉ in the pre-main-sequence phase of stellar evolution. It ends when a star of 0.5 M_☉ or larger develops a radiative zone, or when a smaller star commences nuclear fusion on the main sequence.

T Tauri stars comprise the youngest visible F, G, K and M spectral type stars (<2 M_☉). Their surface temperatures are similar to those of main-sequence stars of the same mass, but they are significantly more luminous because their radii are larger. Their central temperatures are too low for hydrogen fusion. Instead, they are powered by gravitational energy released as the stars contract, while moving towards the main sequence, which they reach after about 100 million years. They typically rotate with a period between one and twelve days, compared to a month for the Sun, and are very active and variable.

There is evidence of large areas of starspot coverage, and they have intense and variable X-ray and radio emissions (approximately 1000 times that of the Sun). Many have extremely powerful stellar winds; some eject gas in high-velocity bipolar jets. Another source of brightness variability are clumps (protoplanets and planetesimals) in the disk surrounding T Tauri stars.>>

johnnydeep wrote: ↑Tue Jan 18, 2022 3:56 pm

neufer wrote: ↑Mon Jan 17, 2022 10:55 pm

Chris Peterson wrote: ↑Mon Jan 17, 2022 9:46 pm

Technically, it's emitting light across the entire EM spectrum, like any thermal source. But it's cool, so the peak wavelength, where there's enough energy to reasonably image, is quite long- probably around 10 micrometers. That said, some dusty regions like this exhibit fluorescence in the deep red, stimulated by local UV sources. Some of the photons captured here might be produced that way. But I suspect most of what we're seeing is reflected light.

The Earth radiates ~10 micrometers. I would imagine that the dust here is much cooler than the Earth.

https://apod.nasa.gov/apod/ap090715.html

According to Wien's Law, stuff at 300 K has a black body radiation spectrum with a peak at 2898 μm⋅K / 300 K = 9.66 μm (micrometers), which is in the IR.

So the question is: just how hot is this interstellar dust?

neufer wrote: ↑Mon Jan 17, 2022 10:55 pm

Chris Peterson wrote: ↑Mon Jan 17, 2022 9:46 pm

johnnydeep wrote: ↑Mon Jan 17, 2022 9:30 pm

Ah, yes, the ever-present filters. So we're not seeing light being emitted from the dust in this photo. But it's still emitting some wavelengths of light due to having a temperature, right? And probably the JWST - among various other IR scopes - could see them in the true light of their own making.

Technically, it's emitting light across the entire EM spectrum, like any thermal source. But it's cool, so the peak wavelength, where there's enough energy to reasonably image, is quite long- probably around 10 micrometers. That said, some dusty regions like this exhibit fluorescence in the deep red, stimulated by local UV sources. Some of the photons captured here might be produced that way. But I suspect most of what we're seeing is reflected light.

The Earth radiates ~10 micrometers. I would imagine that the dust here is much cooler than the Earth.

https://apod.nasa.gov/apod/ap090715.html

jarmoruuth wrote: ↑Tue Jan 18, 2022 6:33 am I have no idea how “official” those nebula names are. The only nebula that I was able to resolve from Sesame Name Resolver was Thumbprint Nebula.

As already mentioned, the Chamaeleon III dark cloud is visible in the image and part of the Chamaeleon II dark cloud is visible at the top of the image. To the right of this image is Chamaeleon I dark cloud.

starsurfer wrote: ↑Mon Jan 17, 2022 11:03 pm
Officially, the bottom half is catalogued as the Chamaeleon III cloud and part of the Chamaeleon II cloud is in the upper half.

Also Thumbprint Nebula is scientifically recognised.
It is worth reading this!

• Me thinks that Chamaeleon I should be the REAL Thumbprint Nebula:

https://en.wikipedia.org/wiki/Chamaeleon_complex wrote:
<<"Chamaeleon III appears to be devoid of current star-formation activity." There are two particularly prominent nebulae associated with this area. The smaller is commonly known as the Thumbprint Nebula and the larger The Talon Nebula.

Chamaeleon II contains the Uhuru source 4U 1302–77. It is close to RXJ 1303.1-7706 at RA 13h 03m 04.70s Dec -77° 06' 55.0", a K7-M0 new WTT. The Chamaeleon II dark cloud contains some 40 X-ray sources. Observation in Chamaeleon II was carried out from September 10 to 17, 1993. Source RXJ 1301.9-7706, a new WTTS candidate of spectral type K1, is closest to 4U 1302–77.

The REAL Thumbprint Nebula?

---

This is a ROSAT false-color image in X-rays between 500 eV and 1.1 keV of the Chamaeleon I dark cloud. The contours are 100 µm emission from dust measured by the IRAS satellite. Credit: D Burrows, J Mendenhall, and E Feigelson Penn State University using the US/German ROSAT satellite.

The Chamaeleon I (Cha I) cloud is one of the nearest active star formation regions at ~160 pc. It is relatively isolated from other star-forming clouds, so it is unlikely that older pre-main sequence (PMS) stars have drifted into the field. The total stellar population is 200–300. The Cha I cloud is further divided into the North cloud or region and South cloud or main cloud.

HD 97300 emits X-rays, illuminates the reflection nebula IC 2631 and is one of the highest mass members of the Cha I cloud, spectral type B9V, a Herbig Ae/Be star without emission lines.

Cha Halpha 1 is an object of spectral type M8 in the Chamaeleon I dark cloud that was determined in 1998 to be an X-ray source and as such is the first X-ray emitting brown dwarf found.

There are some seventy to ninety X-ray sources in the Chamaeleon I star forming region. The Uhuru X-ray source (4U 1119–77) is within the Chamaeleon I cloud. This source region within the Chamaeleon I dark cloud was observed by ROSAT on February 9 at 22:14:47 UTC to February 18, 1991, 17:59:12 UTC, and on March 6, 1991, from 09:12:19 to 13:05:13 UTC. This cloud contains both "weak" T Tauri (WTT) stars and "classical" T Tauri (CTT) stars. Chamaeleon I X-ray ROSAT source 66 is at RA 11h 17m 36.4-37.9s Dec -77° 04' 27-50", is a CTT, Chamaeleon I No. T56, aka CTT star HM 32.

The Chamaeleon I dark cloud was observed with the Imaging Proportional Counter (IPC) on board the Einstein Observatory for 2.5 h on January 23–24, 1981, identifying some 22 X-ray sources.[5] None of these sources was closer than 8' to 4U 1119–77.>>

Chris Peterson wrote: ↑Mon Jan 17, 2022 9:46 pm

johnnydeep wrote: ↑Mon Jan 17, 2022 9:30 pm

Chris Peterson wrote: ↑Mon Jan 17, 2022 9:20 pm
I take it to mean that we're seeing the light reflected from the dust, unlike the usual case where we simply see the dust indirectly by the background light it blocks. At these wavelengths, we're certainly not seeing any radiation emitted by the dust.

Nor do I think we're seeing any near-IR, as all conventional LRGB filters block it.

Ah, yes, the ever-present filters. So we're not seeing light being emitted from the dust in this photo. But it's still emitting some wavelengths of light due to having a temperature, right? And probably the JWST - among various other IR scopes - could see them in the true light of their own making.

Technically, it's emitting light across the entire EM spectrum, like any thermal source. But it's cool, so the peak wavelength, where there's enough energy to reasonably image, is quite long- probably around 10 micrometers. That said, some dusty regions like this exhibit fluorescence in the deep red, stimulated by local UV sources. Some of the photons captured here might be produced that way. But I suspect most of what we're seeing is reflected light.

johnnydeep wrote: ↑Mon Jan 17, 2022 9:30 pm

Chris Peterson wrote: ↑Mon Jan 17, 2022 9:20 pm

johnnydeep wrote: ↑Mon Jan 17, 2022 8:27 pm Trying to figure out the significance of the sentence "In this four-hour exposure, however, the dust is seen mostly in light of its own, with its strong red and near-infrared colors giving creating a brown hue."

What's the definition of "light of its own"? Simply any light- including infrared - that's not reflected from something else? And I guess the point is that, yes, dust is "dark" and certainly isn't fusing matter like stars do, but even so, it nevertheless emits lower energy photons simply because it has a non-zero temperature?

I take it to mean that we're seeing the light reflected from the dust, unlike the usual case where we simply see the dust indirectly by the background light it blocks. At these wavelengths, we're certainly not seeing any radiation emitted by the dust.

Nor do I think we're seeing any near-IR, as all conventional LRGB filters block it.

Ah, yes, the ever-present filters. So we're not seeing light being emitted from the dust in this photo. But it's still emitting some wavelengths of light due to having a temperature, right? And probably the JWST - among various other IR scopes - could see them in the true light of their own making.

Chris Peterson wrote: ↑Mon Jan 17, 2022 9:20 pm

johnnydeep wrote: ↑Mon Jan 17, 2022 8:27 pm Trying to figure out the significance of the sentence "In this four-hour exposure, however, the dust is seen mostly in light of its own, with its strong red and near-infrared colors giving creating a brown hue."

What's the definition of "light of its own"? Simply any light- including infrared - that's not reflected from something else? And I guess the point is that, yes, dust is "dark" and certainly isn't fusing matter like stars do, but even so, it nevertheless emits lower energy photons simply because it has a non-zero temperature?

I take it to mean that we're seeing the light reflected from the dust, unlike the usual case where we simply see the dust indirectly by the background light it blocks. At these wavelengths, we're certainly not seeing any radiation emitted by the dust.

Nor do I think we're seeing any near-IR, as all conventional LRGB filters block it.

johnnydeep wrote: ↑Mon Jan 17, 2022 8:27 pm Trying to figure out the significance of the sentence "In this four-hour exposure, however, the dust is seen mostly in light of its own, with its strong red and near-infrared colors giving creating a brown hue."

What's the definition of "light of its own"? Simply any light- including infrared - that's not reflected from something else? And I guess the point is that, yes, dust is "dark" and certainly isn't fusing matter like stars do, but even so, it nevertheless emits lower energy photons simply because it has a non-zero temperature?

https://en.wikipedia.org/wiki/Local_Bubble wrote:

Click to play embedded YouTube video.

The common chameleon (Chamaeleo chamaeleon) turned black.

---

<<The Local Bubble, or Local Cavity, is a relative cavity in the interstellar medium (ISM) of the Orion Arm in the Milky Way. It contains the closest of celestial neighbours and among others, the Local Interstellar Cloud (which contains the Solar System), the neighbouring G-Cloud, the Ursa Major Moving Group (the closest stellar moving group) and the Hyades (the nearest open cluster). It is at least 300 light years across, and is defined by its neutral-hydrogen density of about 0.05 atoms/cm³, or approximately one tenth of the average for the ISM in the Milky Way (0.5 atoms/cm³), and one sixth that of the Local Interstellar Cloud (0.3 atoms/cm³).

In January 2022, a paper in the journal Nature found that observations and modelling had determined that the action of the expanding surface of the bubble had collected gas and debris and was responsible for the formation of all young, nearby stars.

The exceptionally sparse gas of the Local Bubble is the result of supernovae that exploded within the past ten to twenty million years. The gas remains in an excited state, emitting in the X-ray band. Geminga, a pulsar in the constellation Gemini, was once thought to be the remnant of a single supernova that created the Local Bubble, but now multiple supernovae in subgroup B1 of the Pleiades moving group are thought to have been responsible, becoming a remnant supershell. The Loop I Bubble was cleared, heated and maintained by supernovae and stellar winds in the Scorpius–Centaurus Association, some 500 light years from the Sun. The Loop I Bubble contains the star Antares (Alpha Scorpii). Several tunnels connect the cavities of the Local Bubble with the Loop I Bubble, called the "Lupus Tunnel". In 2019, researchers found interstellar iron in Antarctica which they relate to the Local Interstellar Cloud, which might be related to the formation of the Local Bubble.

Launched in February 2003 and active until April 2008, a small space observatory called Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) examined the hot gas within the Local Bubble. The Local Bubble was also the region of interest for the Extreme Ultraviolet Explorer mission (1992–2001), which examined hot EUV sources within the bubble. Sources beyond the edge of the bubble were identified but attenuated by the denser interstellar medium. In 2019, the first 3D map of the Local Bubble has been reported using the observations of diffuse interstellar bands.>>

jarmoruuth wrote: ↑Mon Jan 17, 2022 7:31 am Thanks, Ann! And thanks for nice comments, they got linked to the APOD text!

With your tips on stars and some additional tips from Robert Nemiroff and other people, I was able to find more details and names for most of the dusty areas in the image. Use mouseover on the web version to see annotations. Nebulae names were listed in a book ‘Chadwick, Stephen; Cooper, Ian. Imaging the Southern Sky’.