[vsnet-alert 10377] YSOs from a Symbiotic Star catalogue

[bydra at Safe-mail.net]

[The list of candidate variables is towards the end of the post]

In Corradi et al A&A 480, 408 (2008) (http://arxiv.org/abs/0712.2391 ) the following Table 1 is given 
<(http://cdsarc.u-strasbg.fr/viz-bin/ftp-index?/ftp/cats/J_A%2bA/480/409>

which according to the abstract at that arxiv site is meant as a list of candidate Symbiotic Stars.  The abstract notes that using Halpha excess sources to find such can have some overlap with Young Stellar Object (YSO) candidates, but that the latter are usually evident from their proximity to star forming regions.  Nevertheless, most of the brightest red magnitude objects in their table of candidate symbiotic stars appear to be in fact YSOs, which is easily shown.  I admittedly haven't bothered to read the full paper, but why there isn't a separate table for firm Symbiotic Star candidates and a table for more uncertain objects is not clear.  Even though IPHAS by its nature hugs the Galactic Plane, the fact that some of these objects are even at |b| < 1 is a big clue, for Symbiotic Stars have a large spread of Galactic Latitude and a preponderence of objects at |b| very near 0 should be at least a little suspicious in any list of such objects.

Nevertheless it is a nice example of the use of colour information.  Ironically the following data comes from the above table 1, where the authors of the paper have actually cross matched IPHAS data with NIR magnitude sources.

http://i38.tinypic.com/6zlahs.jpg

displays again the plot of 2MASS J-Ks as x axis and CMC14 r' - 2MASS J as y axis and the grey dots are objects matched to the GCVS on a one arcsecond radius linkage.

The blue dots are the unreddened dwarf sequence in this colour space for spectral types A to M from table 8 of this paper http://adsabs.harvard.edu/abs/2008MNRAS.388...89G with each dot representing an actual type from that table, and the red dots are the same again for the giant sequence.  The black triangles are the objects from the Symbiotic Star list, above, with magnitudes brighter than r' 14.7.

As J is reddened about two and a half times as much as Ks, normally, whilst red magnitudes are reddened about seven and a half magnitudes as much as Ks for normal interstellar extinction, r' is consequently reddened about three times as much as J, such that reddening in J-Ks causes objects to migrate rightwards on the graph at a slower rate than that which r'-J migrates upwards, magnitude colour difference wise.

Thus objects that are redder than usual in J-Ks but bluer than usual in r'-J are likely to be ones with near infrared (NIR) excess, usually due to circumstellar dust.  Both YSOs and post AGB (post Asymptotic Giant Branch) stars can be surrounded by circumstellar dust, but post AGB stars are red in the first instance.  Although symbiotic stars are combinations of red and blue stars, the red giant star usually dominates the colours at optical and just red of optical passbands, they usually appear red in B-V and J-Ks colours for example.

So, preamble over.  Some of the following brighter than r' 14.7 objects have data in NSVS/ROTSE1 at skydot.lanl.gov, but it is down in the noise, and it is difficult to be sure of any low amplitude variability for either the Symbiotic Stars (and therefore possible ZAND variables) or the YSOs (and therefore possibly Ae/Be variables).  Thus making it a possible longterm project for those interested in studying YSOs both visually and with CCD, as these stars should just be manageable with common amateur equipment as used by variable star observers nowadays.  Some of the objects in the list brighter than 15th mag in r' are in fact known YSO variables (eg MisV1441 for one), with a couple of known ZANDs (eg V1413 Aql), however being either a YSO or a Symbiotic Star does not necessarily mean a star is variable, at least optically.

The following list gives the coordinates and J-Ks colours of the stars of r' <= 14.7, with at times additional comments such as expected type from their placement on the above colour graph, plus extra comments with respect to any known variability.  It is sorted on ascending J-Ks.

Finally it should also be noted that for some of these brighter objects this information is technically already available prior to this 2008 paper, to some extent, as their 2MASS colours are already available, and quite a few of them are already known as Halpha emission line stars in various catalogues, and especially in Kohoutek's Northern Milky Way compilation of said.  The brighter stars are the ones most likely to be observable however, and consequently most likely to have been observed and thus appear in previous Halpha surveys, even if those surveys at times make no claim to stellar type.


coordinates (J2000)      J-Ks

05 18 27.42 +30 08 49.7  0.95

PW Aur - known yso, yet contradictingly appears amongst K giants on the colour plot.  Possibly T Tau as opposed to Herbig Ae/Be?

23 12 44.96 +61 46 05.4  1.05

YSO?

00 10 36.41 +58 50 05.0  1.15

In a region with much nebulosity and possibly an xray source, but colour locale unclear as to which type

19 03 46.84 +16 26 16.9  1.23

Lying amongst the red giants in the GCVS grey dots, and next to the lastmost synthetic colour of the unreddened giant sequence, said dot representing M5 III, this star is a good candidate for a Symbiotic Star.

It is in fact the ZAND star V1413 Aql

20 22 10.20 +33 50 34.6  1.30

Just amongst the red giants on the plot, and in a field fairly free from star formation indications, so a candidate symbiotic.

06 31 10.28 +09 59 17.2	 1.35

Blueward in r'-J yet redward in J-Ks, a good candidate for an Herbig Ae/Be star.  Amidst the diffuse nebulosity IC 447 in Monoceros, also suggestive of being near a star forming region.

It is in fact the known INS variable YSO V482 Mon.

19 26 39.93 +21 07 05.3	 1.37

No firm clues from the field as to which type of star this is, in the colour space it lives in a YSO domain.

19 35 01.31 +13 54 27.5	 1.47

No field clues to speak of, the position on the colour plot suggests slightly reddened red giant, so possible Symbiotic Star.

20 17 08.12 +41 07 27.0  1.50

No field clues to speak of, the position on the colour plot suggests slightly reddened red giant, so possible Symbiotic Star.

20 54 58.07 +47 45 51.7  1.51

No field clues to speak of, the position on the colour plot suggests YSO.

19 32 32.88 +15 17 11.5  1.53

No field clues to speak of, the position on the colour plot suggests YSO.

18 44 39.63 +05 02 49.1  1.58

No field clues to speak of, the position on the colour plot suggests slightly reddened red giant, so possible Symbiotic Star.

It is in fact DQ Ser, type L in the GCVS (irregular long period variable) but included in Symbiotic Star lists in the literature on such objects based on spectroscopic work, so a likely ZAND.

20 57 59.87 +43 53 26.1  1.60

Strong field indicators towards it being a YSO, a strongly YSO position on the colour plot http://i38.tinypic.com/6zlahs.jpg .

It is in fact the nebulosity involved T Tau star V1539 Cyg.

Interesting to note on this one that the spectral type of K6e for this object parallels the synthetic giant stars' sequence for late K, but is strongly due right, suggesting little if any extra redness in r'-J and thus that most if not all the J-Ks extra redness for this object is likely near infrared excess due to circumsteller material.

23 57 34.77 +64 46 49.1  1.61

Several field indicators towards it being a YSO, a strongly YSO position on the colour plot http://i38.tinypic.com/6zlahs.jpg , and also admittedly loose indications from its MSX6C and IRAS fluxes.

It is in fact the nebulosity involved T Tau star V522 Cas.

Note the J-Ks for this YSO object is the same as for the next object.

19 30 38.84 +18 39 09.8  1.61

No field clues to speak of, although there are some not too distant star forming regions, however the position on the colour plot suggests slightly reddened red giant, so a possible Symbiotic Star.

Note the J-Ks for this YSO object is the same as for the preceding object.

21 00 21.42 +52 27 09.6  1.75

Colours say YSO.  However, this is a relatively close five arcsec pair with a similar magnitude nearby star, so possible cross matching errors have to be considered.

Within half an arcminute of the next object.

21 00 19.06 +52 27 28.3  1.88

Colours say YSO.

Within half an arcminute of the preceding object.

19 42 54.98 +23 24 14.9  1.89

>From this star onwards to the end of the list the colours say YSO candidates.

02 34 10.28 +61 24 40.4  1.93

YSO:  Likely also an xray source.

22 47 22.39 +58 01 21.5  1.95

YSO?  Flux increases at longer wavelengths (msx6c, iras) suggestive of surrounding material, and despite being optically quite faint is an xray source (2xmm).

23 03 46.02 +61 48 46.2  2.03

YSO:

23 59 19.98 +66 23 12.0  2.07

YSO:

It is in fact suspected variable NSV 14794, given a probable YSO variability type classification of IN:

02 47 48.61 +60 57 50.4  2.08

YSO:

19 25 38.41 +22 34 14.6  2.18

YSO:

02 29 35.91 +61 15 56.8  2.20

YSO:

19 57 12.42 +30 13 16.1  2.20

YSO:

22 18 08.49 +56 05 53.3  2.35

YSO:

23 13 07.09 +59 02 47.9  2.40

YSO:

21 33 17.78 +57 48 13.5  2.42

YSO:

It is in fact LT Cep, which is classified as a possible RR Lyrae variable in the GCVS.

Noted earlier was the fact that interstellar extinction would cause objects to migrate upward as well as rightward in the colour plot, so this is goodly evidence that the variability type of this star in the literature is in error.

A revision project for someone wishing to correct this error with long term monitoring.

Incidentally, this optically faint source being also an MSX6C and IRAS mid and far infrared source strongly precludes a Halo A to F star such as a RR Lyrae star would be, so even if not a YSO, certainly not an RR Lyr.

20 47 13.69 +46 35 17.5  2.57

YSO:

The "orphaned" (ie no obvious optical counterpart at the immediate position) object NSV 13301, noted as having spectral type Ke, appropriate for a T Tau star, lies half an arcminute away, and likely these two objects are the same.

19 44 05.25 +23 26 47.9  2.69

YSO:

03 20 39.49 +56 23 58.2  2.73

YSO:


A further object included in the Symbiotic Stars list is MisV 1441, which with J-Ks 4.3 and r'-J 0.6 is very strongly away from the red giant line of the colour plot (off the J-Ks scale in fact for that particular graph).  With r' 14.8 and discovered from amateur images using unfiltered red sensistive CCDs it shows that the brighter objects in this Symbiotic Star Catalogue that are likely to be YSOs can readily be monitored for variability.  And those that aren't YSOs but Symbiotic Stars may also kindly reveal a variable or two (although not necessarily so).

A little bit of simplest astrophysics goes a fairly long way.

John Greaves