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ASTRO: NGC 1579
NGC 1579 Image down sampled 0.5x
Perseus Penryn, California October 2008 M 250 @ f 9.3 (ag, ST-4) ST-10XME LRGB - 10 minute subs A large area of dust. NGC 1579 is a reflection nebula illuminated by the young and bright emission line star LkH-alpha 101. It is this star that provides the intense red color. There is a tendecy to label this nebula as an emission/reflection nebula. All peer-reviewed scientific studies support the conclusion that NGC 1579 is a cold cloud of dust reflecting the intense h-alpha light of 'LkH-alpha 101'. Redman, et.al. (1986) conducted polarization studies to determine the illuminating source. The abstract from that study follows; "The linear polarization of the reflection nebula NGC 1579 and the CO (1 to 0) emission from the associated molecular gas have been mapped for several minutes of arc around the exciting star LkH-alpha 101. These maps show conclusively that LkH-alpha 101 is the sole significant source of illumination in the region. The dust in the reflection nebula appears to be uniform over the illuminated region and is uniformly illuminated by LkH-alpha 101. Despite the patchy obscuration, the dark cloud which obscures LkH-alpha 101 does not surround the star. LkH-alpha 101 may have formed out of a placental cloud whose remnants now include four molecular cloud fragments, two in front of and two behind the reflection nebula, as well as an H I cloud previously detected in the region." Herbirg, et.al. (2004) reports; "The central region of the dark cloud L1482 is illuminated by LkHalpha 101, a heavily reddened (AV~10 mag) high-luminosity (=8×103 Lsolar) star having an unusual emission-line spectrum plus a featureless continuum. About 35 much fainter (mostly between R=16 and 21) Halpha emitters have been found in the cloud. Their color-magnitude distribution suggests a median age of about 0.5 Myr, with considerable dispersion. There are also at least five bright B-type stars in the cloud, presumably of about the same age; none show the peculiarities expected of HAeBe stars. Dereddened, their apparent V magnitudes lead to a distance of about 700 pc. Radio observations suggest that the optical object LkHalpha 101 is in fact a hot star surrounded by a small H II region, both inside an optically thick dust shell. The level of ionization inferred from the shape of the radio continuum corresponds to a Lyman continuum luminosity appropriate for an early B-type zero-age main-sequence star. The V-I color is consistent with a heavily reddened star of that type. However, the optical spectrum does not conform to this expectation: the absorption lines of an OB star are not detected. Also, the [O III] lines of an H II region are absent, possibly because those upper levels are collisionally deexcited at high densities. There are several distinct contributors to the optical spectrum of LkHalpha 101. The Halpha emission line is very strong, with wings extending to about +/-1700 km s-1, which could be produced by a thin overlying layer of hot electron scatterers. There is no sign of P Cygni type mass ejection. Lines of Si II are narrower, while the many Fe II lines are still narrower and are double with a splitting of about 20 km s-1. Lines of [Fe II], [O I], and [S II] are similarly sharp but are single, at the same velocity as the Fe II average. Work by Tuthill et al. allowed the inference, from K-band interferometry, that the central source is actually a small horseshoe-shaped arc about 0.05" (35 AU) across. A tipped annulus of that size in rotation about a 15 Msolar star would produce double spectrum lines having about the splitting observed for Fe II. The totality of observational evidence encourages the belief that LkHalpha 101 is a massive star caught in an early evolutionary state." |
#2
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ASTRO: NGC 1579
On 11/12/2010 1:36 PM, glen youman wrote:
NGC 1579 Image down sampled 0.5x Perseus Penryn, California October 2008 M 250 @ f 9.3 (ag, ST-4) ST-10XME LRGB - 10 minute subs A large area of dust. NGC 1579 is a reflection nebula illuminated by the young and bright emission line star LkH-alpha 101. It is this star that provides the intense red color. There is a tendecy to label this nebula as an emission/reflection nebula. All peer-reviewed scientific studies support the conclusion that NGC 1579 is a cold cloud of dust reflecting the intense h-alpha light of 'LkH-alpha 101'. Redman, et.al. (1986) conducted polarization studies to determine the illuminating source. The abstract from that study follows; "The linear polarization of the reflection nebula NGC 1579 and the CO (1 to 0) emission from the associated molecular gas have been mapped for several minutes of arc around the exciting star LkH-alpha 101. These maps show conclusively that LkH-alpha 101 is the sole significant source of illumination in the region. The dust in the reflection nebula appears to be uniform over the illuminated region and is uniformly illuminated by LkH-alpha 101. Despite the patchy obscuration, the dark cloud which obscures LkH-alpha 101 does not surround the star. LkH-alpha 101 may have formed out of a placental cloud whose remnants now include four molecular cloud fragments, two in front of and two behind the reflection nebula, as well as an H I cloud previously detected in the region." Herbirg, et.al. (2004) reports; "The central region of the dark cloud L1482 is illuminated by LkHalpha 101, a heavily reddened (AV~10 mag) high-luminosity (=8×103 Lsolar) star having an unusual emission-line spectrum plus a featureless continuum. About 35 much fainter (mostly between R=16 and21) Halpha emitters have been found in the cloud. Their color-magnitude distribution suggests a median age of about 0.5 Myr, with considerable dispersion. There are also at least five bright B-type stars in the cloud, presumably of about the same age; none show the peculiarities expected of HAeBe stars. Dereddened, their apparent V magnitudes lead to a distance of about 700 pc. Radio observations suggest that the optical object LkHalpha 101 is in fact a hot star surrounded by a small H II region, both inside an optically thick dust shell. The level of ionization inferred from the shape of the radio continuum corresponds to a Lyman continuum luminosity appropriate for an early B-type zero-age main-sequence star. The V-I color is consistent with a heavily reddened star of that type. However, the optical spectrum does not conform to this expectation: the absorption lines of an OB star are not detected. Also, the [O III] lines of an H II region are absent, possibly because those upper levels are collisionally deexcited at high densities. There are several distinct contributors to the optical spectrum of LkHalpha 101. The Halpha emission line is very strong, with wings extending to about +/-1700 km s-1, which could be produced by a thin overlying layer of hot electron scatterers. There is no sign of P Cygni type mass ejection. Lines of Si II are narrower, while the many Fe II lines are still narrower and are double with a splitting of about 20 km s-1. Lines of [Fe II], [O I], and [S II] are similarly sharp but are single, at the same velocity as the Fe II average. Work by Tuthill et al. allowed the inference, from K-band interferometry, that the central source is actually a small horseshoe-shaped arc about 0.05" (35 AU) across. A tipped annulus of that size in rotation about a 15 Msolar star would produce double spectrum lines having about the splitting observed for Fe II. The totality of observational evidence encourages the belief that LkHalpha 101 is a massive star caught in an early evolutionary state." This is another I need to revisit. Mine looks horrid compared to this, especially as to noise and color. Took it as one of my very first objects after going digital. I had no idea what I was doing back then. Used only 5 minute subs which just doesn't cut it with only 6 of them. 3 ten minute ones are far better and the 4 I usually use nearly half the noise of 6 five minute ones and go deeper. I had a devil of a time with the color. Figured it was my limited skills, and it was. But at the time hadn't realized it wasn't a true emission object and was trying to get the h alpha pink that just wouldn't quite show. Rather than reprocess it I need to redo the data. Of course our rainy October is just now showing up a month late. Won't be any imaging for a while if the weather reports are right. Snow and rain mix for the next two weeks. Did finish getting the blower on the Ranger ATV today so that should keep the snow at bay for a few more weeks. Rick -- Correct domain name is arvig and it is net not com. Prefix is correct. Third character is a zero rather than a capital "Oh". |
#3
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ASTRO: NGC 1579
I first imaged ngc 1579 with film and one look at the result had me
scrambling to find out what type nebula I had imaged, it was obvious it was not an emission nebula. There was a French astrophotograper with perhaps the best image I've seen. I've searched for that image and couldn't find it (google). Forecast here is for clear skys, of course that will change the day after full moon. On Fri, 12 Nov 2010 15:26:54 -0600, Rick Johnson wrote: This is another I need to revisit. Mine looks horrid compared to this, especially as to noise and color. Took it as one of my very first objects after going digital. I had no idea what I was doing back then. Used only 5 minute subs which just doesn't cut it with only 6 of them. 3 ten minute ones are far better and the 4 I usually use nearly half the noise of 6 five minute ones and go deeper. I had a devil of a time with the color. Figured it was my limited skills, and it was. But at the time hadn't realized it wasn't a true emission object and was trying to get the h alpha pink that just wouldn't quite show. Rather than reprocess it I need to redo the data. Of course our rainy October is just now showing up a month late. Won't be any imaging for a while if the weather reports are right. Snow and rain mix for the next two weeks. Did finish getting the blower on the Ranger ATV today so that should keep the snow at bay for a few more weeks. Rick |
#4
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ASTRO: NGC 1579
Glen, you got a lot more signal than I was able to get of this object so
far. And detail is very good also. Stefan "glen youman" schrieb im Newsbeitrag ... NGC 1579 Image down sampled 0.5x Perseus Penryn, California October 2008 M 250 @ f 9.3 (ag, ST-4) ST-10XME LRGB - 10 minute subs A large area of dust. NGC 1579 is a reflection nebula illuminated by the young and bright emission line star LkH-alpha 101. It is this star that provides the intense red color. There is a tendecy to label this nebula as an emission/reflection nebula. All peer-reviewed scientific studies support the conclusion that NGC 1579 is a cold cloud of dust reflecting the intense h-alpha light of 'LkH-alpha 101'. Redman, et.al. (1986) conducted polarization studies to determine the illuminating source. The abstract from that study follows; "The linear polarization of the reflection nebula NGC 1579 and the CO (1 to 0) emission from the associated molecular gas have been mapped for several minutes of arc around the exciting star LkH-alpha 101. These maps show conclusively that LkH-alpha 101 is the sole significant source of illumination in the region. The dust in the reflection nebula appears to be uniform over the illuminated region and is uniformly illuminated by LkH-alpha 101. Despite the patchy obscuration, the dark cloud which obscures LkH-alpha 101 does not surround the star. LkH-alpha 101 may have formed out of a placental cloud whose remnants now include four molecular cloud fragments, two in front of and two behind the reflection nebula, as well as an H I cloud previously detected in the region." Herbirg, et.al. (2004) reports; "The central region of the dark cloud L1482 is illuminated by LkHalpha 101, a heavily reddened (AV~10 mag) high-luminosity (=8×103 Lsolar) star having an unusual emission-line spectrum plus a featureless continuum. About 35 much fainter (mostly between R=16 and 21) Halpha emitters have been found in the cloud. Their color-magnitude distribution suggests a median age of about 0.5 Myr, with considerable dispersion. There are also at least five bright B-type stars in the cloud, presumably of about the same age; none show the peculiarities expected of HAeBe stars. Dereddened, their apparent V magnitudes lead to a distance of about 700 pc. Radio observations suggest that the optical object LkHalpha 101 is in fact a hot star surrounded by a small H II region, both inside an optically thick dust shell. The level of ionization inferred from the shape of the radio continuum corresponds to a Lyman continuum luminosity appropriate for an early B-type zero-age main-sequence star. The V-I color is consistent with a heavily reddened star of that type. However, the optical spectrum does not conform to this expectation: the absorption lines of an OB star are not detected. Also, the [O III] lines of an H II region are absent, possibly because those upper levels are collisionally deexcited at high densities. There are several distinct contributors to the optical spectrum of LkHalpha 101. The Halpha emission line is very strong, with wings extending to about +/-1700 km s-1, which could be produced by a thin overlying layer of hot electron scatterers. There is no sign of P Cygni type mass ejection. Lines of Si II are narrower, while the many Fe II lines are still narrower and are double with a splitting of about 20 km s-1. Lines of [Fe II], [O I], and [S II] are similarly sharp but are single, at the same velocity as the Fe II average. Work by Tuthill et al. allowed the inference, from K-band interferometry, that the central source is actually a small horseshoe-shaped arc about 0.05" (35 AU) across. A tipped annulus of that size in rotation about a 15 Msolar star would produce double spectrum lines having about the splitting observed for Fe II. The totality of observational evidence encourages the belief that LkHalpha 101 is a massive star caught in an early evolutionary state." |
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